Maybe the actual scene where Vader takes a dive could be edited out (though that could create problems, as Vader would go from standing up to down on his knees in the next shot), and the hacking Luke does could be edited so Luke takes out Vader's forearm almost immediately after he knocks him down.

It would be hard, but could Vader's fall from the carbonite chamber be used from EMPIRE in this way: there is the far shot showing Luke beating Vader back to the elevator; cut to a static shot showing Luke raising his hand (or making another gesture) and take Vader's fall and move it sideways to imply him being propelled into the elevator door; cut to Luke beating on Vader, who is now on his back; cut out some of Luke beating on Vader's lightsabre (as Vader is just holding it out) and maybe cut Vader's forearm off in the 1st or 2nd hit.