You need to make Yoda act like a muppet. Being him dubbed by Oz means you can use Fozzie's lines as you wish!

Also, since I saw ROTJ the first time, I always pictured Yoda's last words like this:

Luke... remember to switch off the lights....

Luke... don't forget to shut the windows, or you'll get a cold...!

Luke... make sure to turn off gas...

(Luke goes away)

Luke... Luke, come here...

If you want to do it, you'll definitely need to find Fozzie's dialogues. You can find something in line in the movie "Muppets from Space":

Fozzie the Bear:"Of course I did. Mom said, always wash your hands."
Kermit the Frog:"Yes, but not when you're wearing invisibility spray!"
Fozzie the Bear:"Mom said, no exceptions."

So you could make "Luke..." + "always wash your hands.", or something.

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Make Yoda annoying, constantly complaining about everything until the end of the movie: "(He's) too old!", "Rest I need" and so on!

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Make Han make more troubles: he is spotted stepping on a root, right? Well, make him so that he's also the one who triggers the ewoks' trap:

Han: (whatever line)

Luke: No, wait!

(the trap is triggered)

Chewie: Graargh!

Han: It's not my fault! (ESB)

You could also make him more jealous of Luke, and so paranoid when they need to pass the emperial blockade that he wants to run away!