Ziz said:

Alternate idea - instead of showing DSII at the end of Empire, just imply that that's where the fleet is headed after the Falcon escapes them at Bespin.

Falcon goes to hyperspace.
Vader pondering what just happened.

Vader (walking down the length of the bridge): "Admiral Piett, set your course for the Endor system."
Piett (as Vader crosses in front of him): "Yes, Lord Vader."

Fleet goes to hyperspace.
Continue with ending of film as it exists.

If the timing is right, you won't even have to worry about lip sync. With Vader, it's just a matter of pacing for how fast he walks vs how fast the line is, and with Piett, it's a short enough line that he should be able to get it off during that second or so that Vader's cape blocks our view of him.

We don't need to see DSII. For the people who know what happens at the opening of Jedi, this scene is an easter egg. For people who don't know (kids of the future), it will give them something to reference back to when they do see Jedi... "Ah, so THAT'S why the fleet went to Endor at the end of Empire!"

This way, the implication is that DSII has been under construction for a while and going there is just a matter of "getting on with business".

But we don't actually need any of this for a reference back when watching Jedi. This has already been set into place with the ending as it exists now. The reference to the search for han, jabba the hutt & the rendezvous at Tatooine does this perfectly. Also the rebel fleet aren't heading to Endor at the end of ESB. They don't even know where the Death Star is being built or even if there is a new one. The rebel fleet are massing near sullust and the Bothan spies get the info for the rebels.

There is no need to add any sort of additional scenes in ESB. This movie is most flawless one in the whole saga (minus cosmetic improvements and a bit of de-SEing). Adding the DS2 or any mention of it (or endor) is totally unnecessary and steps into GL's SE changes territory in that its been put in just because it can.