No, it's not the only way, but it's a valid way to go. Bounce down a few tracks based on scenes and start a new project, then import the video and the new tracks -- it will suck for mixing, but you won't lose the old project.

Another solution is to break your current project apart by scene -- it won't require bouncing down, and it will free up any other tracks that are being used by another scene.

If your computer can handle it (and after 255 tracks, I can understand why it might not), consider ReWire options -- I've used both Ableton Live and Cockos Reaper in slave mode with varying levels of success. Some programs, like Sonar, will require at least a stereo track for the i/o from the ReWire slave, which might mean cleaning up a couple tracks from your 255, but then it opens up a lot more.

As for Logic-specific solutions... I'm a PC guy, so, I don't have any. Sorry.