If you compress a background track (i.e. take the volume of the peaks down) without raising the overall volume of the track, you will, in effect, make the track a bit quieter. The more you compress, the quieter (and less dynamic) the track will become. The bulk of the sound will still be there, but it won't jump out at you during the louder parts.
Squashing the dynamics of backing parts is probably a decent way of making them less noticeable but still present. Watch that you don't kill them, though. Its pretty easy to do.
Take care,
Chris