The wampa attack, I'm sorry to say, could not possibly be seen by--and by anyone, unfortunately--because it was never finished. During filming, the logistics were so problematic that they literally gave up and moved on. So the wampa sequences can never be seen because all that consists is literally a few b-roll shots of soliders reacting and one or two botched close-ups. The sequence can never be seen in its entirety and as a part of the film because narratively it is incomplete.
Han solo's torture and him and Leia kissing on Bespin you probably remember because these things happen in the film! The footage cut for the Leia kiss was from an alternative scene that was re-filmed and would have not appeared past the first rough cut that was assembled mid-way through production (if in fact it made any cut at all). Stuff like the bacta mask and fluid is easy to see that its just exaggerated memories, especially when these shots appeared priminently in the theatrical trailer for film.
Additionally, i believe the rough cut of Empire may still have been made on black and white workprint stock at that time, so obviously the rough cut could not possibly have been screened. Especially being 70mm, you would have to constructed a brand new Interpositive made from the original negatives. Things like this are a big deal--they dont just happen by accident, or "sneak out". There was never any preview screenings with changed footage, and certainly none in 70mm that just happened to make their way to a solitary theater in Edmonton that was only witnessed by a ten year old and his friends. As i said, the very nature of most of these cut scenes makes it impossible for them to have ever gotten out, and they haven't, which is why Lucasfilm has never released them, referenced them or confirmed them in their meticulous "what has changed" lists. To get these scenes would require going back to the original negatives from the archives. Again, I'm not saying that you are crazy or a liar or anything--these types of things are actually common amongst fans, who claim to remember all sorts of alternative versions of the films. I can't say for sure what the source is for these mis-rememberences--kids remember things in very funny ways. Theres a very amusing thread on TFN thats about 50 pages long called "Misconceptions you had about Star Wars when you were a kid" and its filled with all kinds of mis-interpretations of scenes and such.