You know, the GUI necessary to make it possible to create both your desired configuration and the default policy is way beyond GTK's dynamic form capabilities. Since you've got specific desires that you can explain in detail, you'll surely do better with gconf than any possible dialog box. The best configuration system, in my opinion, is to give the user the choice of a few provided policies (for people who don't want to think about configuring this particular aspect) plus the ability to use a user-generated policy (for people who want to come up with one). Madness lies in trying to provide users who think through their policies with a simple choice of the policy they'd come up with.
Your laptop doesn't have any multimedia keys? All of the computers I've bought have at least had a Pause/Break key. Of course, it took a certain amount of cleverness to get it to actually control anything.