Building on what Katherine suggested, how about creating a completely separate system for the fun stuff? Buy yourself a snoopy notebook and use crayons to keep the lists. OK, the crayons may be a bit much, but the idea is to make your fun lists, well, fun. Keeping them completely separate from your "work" stuff will help create some cognitive distance from your work lists, but will still allow you the benefits of GTD. These lists should be approached from a "could do" instead of a "must do" perspective.
Eventually, I think you'll get sick of maintaining two separate systems, but will not want to give up the benefits of having everything out of your head. At that point you'll be able to combine the two systems, and the emotional leap between work and fun won't be nearly as great.
Personally, I would be cautious of only capturing a subset of your stuff -- it can only compromise the trustworthiness of your system.
Best of luck.