It would, however, require the elimination of the first Death Star battle from ANH, which is quite a loss. It would also require that that perhaps all footage of the DS from ANH be altered so that the DS is actually the under-construction one from ROTJ. Not a huge job but some minor skill is needed. Then, perhaps all the DS footage from ROTJ would have to be altered so that the DS is actually the complete one from ANH. Much trickier here since it is seen so much and because of all the activity and ships around it.
As an alternative to losing the Battle of Yavin in ANH you could either eliminate the space battle from ROTJ, or combine them--once the shield goes down some of the Yavin battle footage could be used. This however, is kinda pointless, since Luke is not part of the battle and the Lando footage already is long enough.
A more ambitous and interesting one is make all three films into one three hour film. Replace the DS with the ROTJ one, cut out a few minutes of the Death Star rescue footage from ANH, plus the TIE fighter fight that follows, plus the Yavin battle. So now ANH is roughly 90 minutes long. From here, perhaps go to the Echo base escape, maybe making it seem like the fighters are fleeing the Yavin base, and put the Obi Wan instructions about Dagobah as voice-over in Luke's head (a nice substitue for the voice-over in ANH, since the Yavin battle is now gone and this is what is replacing it). Now comes the tricky part. Eliminate everything after the asteroid chase, but keep anything involving the characters (ie the romance), and keep all of Luke's Jedi training. Now you have to jump mid-ESB to mid-ROTJ. The entire Bespin section is elminated as well as all of the Jabba the Hutt sequence. Han solo isnt frozen and rescued and Vader and Luke don't duel. Instead, Luke's jedi training continues as it does--however, the father-revelation is needed. So, expand Luke confrontation with Vader in the cave. This obviously changes the meaning of the sequence somewhat, and it sounds clumsely and nonsensical but I'm sure with some tinkering and clever writing it could be possible to have the phantom-Vader reveal to Luke the fatherhood secret. Luke emerges and talks to Yoda about it in the ROTJ scene. Maybe some kind of flash-forward would have to be used for this, as if Luke has now completed his training and is now a Jedi (hence the new black uniform). Then Yoda confirms what Luke learned before in the cave--perhaps this was Yodas way of telling Luke to prepare him for his duel with Vader. Obi Wan's subsequent conversation would have to be edited to remove "face vader AGAIN" to just "you must face Vader."
Then Luke finds the rebel fleet and meets up with them. They are just getting ready to finally destroy the death star. Alter it so that it is the completed one from ANH. The rest of the film proceeds mostly as in the final film, but with some minor editing maybe to take down the run time (I'm thinking Ewoks here).
The final product would be just over three hours. Unfortunately most of ESB is lost, but stuff like that is inevitable when making a 7-hour trilogy into a 3-hour movie. But i think my outline is very, very feasible and would be very interesting. I would do it myself but i have yet to solve the whole "using MPEG-2/DVD with Adobe Premiere" thing.