The solution would be to either meticulously paint out the credits or somehow obtain a creditless film print 9i.e an original print before the credits were addedd in PP), neither of which are easy options, but having seen what goes on in the preservation section of this site I have no doubt that somebody could do it if they were so inclined.
A 6hr non-stop BTTF movie would be f**king ace though! The next chance I get, I'm gonna watch all 3 in a row.