I wonder if the NHLPA could do an exhibition game on their own without the NHLs involvement?
Absolutely, as long as they didn't wear NHL merchandise or market it as NHL-sanctioned and whatnot. They could do it for charity. Would have to modify the rules to turn it into more of a shinny/All Star match with no contact, for insurance reasons.
It would actually be a great PR move for the NHLPA and I'm sure the players are jonesing for a game. It wouldn't even have to be those two NHL teams, they could just have a bunch of locked out, established NHLers make all-star teams and give the fans the hockey they were promised.