When Did He Figure It Out

The way the story is popularily understood, Yosef's brothers remain clueless as to his real identity until he shouts out "I'm Yosef, does my father yet live?" at the beginning of last week's parashah.  While that makes for a great climax to a suspenseful story, is it necessarily true?
Rav Yehonasan Eibeshutz zt"l, in his commentary on the section, doesn't think so.  In fact, he has a fascinating alternate approach that explains many of the difficulties in the Torah's narrative just before the big reveal.
First there's the matter of two consecutive, yet contradictory verses:
"With whomsoever of thy servants it be found, both let him die, and we also will be my lord's bondmen. And he said, Now also let it be according unto your words: he with whom it is found shall be my servant; and ye shall be blameless." (Ber 44:9-10)
How can the Egyptian emmisary start off by saying that the brothers' assessment of the penalty was correct but then repeat back to them an entirely different punishment?  What's more, why does Yosef echo that same assessment when the brothers change their mind and announce that they'll all stay as slaves (without mentioning an execution)?
Then there's the matter of Yehudah approaching Yosef directly to speak to him.  Recall that until this point there has been an interpreter standing between Yosef and the brothers at all times.  For all they know, Yosef doesn't understand a word of Hebrew and we have no evidence that the brothers knew Egyptian so how does Yehudah expect to directly communicate with the viceroy?
Consider Rashi's comment (from the Midrash) on Yehudah's line that Yosef is like Pharoah.  Rashi says that just as Pharoah decrees and doesn't fulfill, so you too decree and don't fulfill.  Where do we find that Pharoah didn't keep his own law?
Finally there's the content of Yehudah's speech.  He constantly refers to his father as "thy servant".  Once might be nice for protocol but he keeps doing it even though Yaakov is not a servant of any Egyptian, living as a free landowner in Canaan. 
Rav Eibeshutz therefore brings a new understanding to this part of the story.  He begins by noting all these discrepancies and then adds a further one - according to Chazal, Shimon was imprisoned by Yosef when the brothers were earlier released to go and bring food back to their families but was released from jail and treated honourably after they had departed.  Now that Shimon had been reunited with them, is there any doubt that he would have told the brothers about this curious turn of events?
Rav Eibershutz writes that when the brothers were stopped on their way out of Egypt and accused of stealing Yosef's goblet, the penny finally dropped for Yehudah.  What did is was the problematic response to the brothers offering themselves as slaves while suggesting the thief would be executed.  That penalty would have been the norm under the laws of Bnei Noach.  The :Egyptian -according to some opinions it was Menashe - responded by saying "No, we'll do it your way.  You're B'nai Yisrael so your law is the theif is sold into slavery for his theft and there is no penalty for the accomplices.  I'll take Binyamin back and the rest of your go home."
Now think back to the midrash on the reason for the conflict between Yosef and his brothers in their youth.  Chazal tell us that one of the differences between them was the understanding of their current legal status.  The brothers felt that since they were now living as a complete family in Israel, they had achieved the status of B'nai Yisrael and therefore had to observe halacha.  Yosef, on the other hand, held that until the Torah was actually given their status remained that of B'nai Noach.
And here was the interpreter telling them, in essence: Yes the penalty should be as your said but according to your law, only Binyamin is guilty.  How would some Egyptian interpreter know Torah law?  What's more, why was he being selective with halacha?  After all, the complete law is that that thief has to make proper compensation and only if he can't is he sold into slavery.  The brothers surely had enough money to pay appropriate damages to the Egyptian viceroy.  Why jump straight to slavery?
As a result, Rav Eibeshutz says that Yehudah finally figured out what was happening and who the menacing viceroy really way.  That's why he demanded to speak to Yosef face to face, in order to call his bluff.  He approached him and spoke directly in Hebrew.  Yosef might have initially tried to pretend he didn't understand, and at another point might have claimed that Yehudah's belief that he was Yosef was ridiculous.  After all, Yosef was sold as a slave to Egypt and Egyptian law, according to Chazal, forbid slaves from ever holding a ruling position.
Now Rashi's midrash excerpt makes sense.  Yehudah, sure of Yosef's real identity, points out that Yosef has indeed risen from slave to rule in violation of Egyptian law because Pharoah overrode the law.  Just as Pharoah decreed and didn't keep his own rule, so Yosef was under no obligation to demand Binyamin as his slave.
Therefore it was for this reason that Yosef now revealed himself.  According to Rav Eibeshutz, it wasn't because of overwhelming emotions.  He knew the game was up and that Yehudah had figured things out!