You know what's really strange? Although Epic won't release the JJ2 source code, they already released the Unreal Tournament source code to a group of talented coders in the community. Look at this: http://www.utpg.org/
If someone were to send them a polite email saying "You released the source for one of your most popular games, why not JJ2?" There might be half of almost nearly partly a chance that Epic would even READ IT.

It says this on that site I mentioned. Quite interesting:

We are a group of programmers and server admins from the UT community who got together and approached Epic about the possibility of maintaining the Unreal Tournament code base. Since our goal of maintaining the game and fixing obvious problems, while keeping all the major game-play systems 100% intact, were right along with Epic's goals, Epic granted us access to the source which allows us to undertake this project. Our focus is general maintenance with some of our time spent dealing with security issues in the Unreal Tournament engine.

Annoying, eh? Oh well.