A full day just for Jam? That sounds amazing...does that mean that you teach the class more than once during the day?
What we have done in the past/do right now: when we hard launch Jam, we typically do it it on a Friday night, and turn the place into a club. We have a small happy hour (45 mins) before, where everyone can get to know each other and get comfortable, do the release, and then have the after party. You can hand out passes, you can recruit some of your big Pump instructors to be "bouncers," and of course you have to wear your hottest Jam outfit!
I haven't seen 44 yet (still stalking the mailman), but some things that we have thought about: usually our launches follow a theme, and it can be anything from reality TV (Survivor, Deal or No Deal?, etc.) to movies, to Totally Les Mills. One that I heard about that I still want to do: if you have ever seen Project Runway, they have that giant white screen that the models stand behind before they walk the runway. Set up a couple of those with some backlights, and get your instructors back there posing or dancing the track. Hot! For Deal or No Deal, have the instructors be the models and in the briefcases are the names of the tracks/names of the blocks in the new release. You can even have your gym chip in some merchandise to give away.
I think the most important thing is to get creative and do something that will draw a crowd. Don't be afraid to go all out, because your participants can tell when you have put the extra effort in, and they respond in kind. Keep us posted how it goes! With pics!