Here is a mix of my and chainsaws ideas

I would almost piss in my pants if I saw Boba Fett crawling out of sarlacc and calling his ship via his arm band Check wookiieepedia his armour contacts his ship. And have him blast out.

Then chainsaws idea have him sell the plans to the rebels. BUT REMEMBER TO REMOVE MON MOTHMAS LINE ABOUT PEOPLE DYING TO GET THE PLANS.

Then here is another idea have him head toward the death star remember to play his theme (It is called attacking a star destroyer on the ESB soundtrack) BUT just leave it at him going. This will be before the battle begins. Make it seem like he was working for the emperor but suspensfuly. Any way to have him in the movie more is a good thing.

Here is a take it or leave it thing. We could have boba fett get tangled into the battle of endor and attack the millenium falcon thinking that all of the rebels (han LUKE leia and chewie) are on the ship BUT get plucked by one of the rebels. and either make him eject from his ship because his armour holds oxygen and jetpack away. DIE. or his ship spin away ripping off A New Hope.