Darth Lars said:

No, I think that Yoda being in the PT was absolutely compulsory. Just has Luke is compulsory in the ST. There are too strong hints in the OT to what the character did/will do. I think that more fans would have got outraged if Yoda wasn't in the PT than they are of how Yoda was portrayed.

How about an exchange like this:

Anakin: "I don't understand why we're just waiting here! There won't be a Republic if we don't attack! "

Obi-wan: "Our orders are to stand by."

Anakin: (stews in frustration)

Obi-wan: "It is at times like this that I meditate on what my master taught me, about patience."

Anakin: "You've never mentioned your master before. Who was he?"

Obi-wan: "He was wise and powerful, old even when I first knew him. It was because of him that I became a Jedi."

Anakin: "I'd like to meet him someday."

Obi-wan: "You won't. He was old even when I knew him, living on an uninhabited planet in the outer rim. I was the last of his students. He will train Jedi no more."

That's all I required from the prequels about Yoda. Just a bit of explanation, if that.