Are they groups of friends or general interest groups? I created a fake profile where I just join groups I'm interested in, and it's worked pretty well. It's just about the only way I use Facebook these days - I only check my "real" profile once every 2-4 weeks for a minute or two to see if I received any messages.

The only downside is some groups won't accept you if you don't have any friends, but there doesn't seem to be many like that.