I wish I could say: "Hey, I've got one of those, and it works like this ... "
But the best I can offer is this little nugget I found for integrating keymaps straight into the raw X config files:
Basically if you can use xev to retrieve your scancodes, then this method should work - and work without any external programs. I don't know what affects the scancode retrieval, but xev will quickly reveal whether or not X is getting the button calls.
It says it's for XFree86, but works fine for xorg (no suprise there) and I've tested it with Slack 9.1, 10.1 and Slamd64.
All the best,