I've messed with the registry to tell mouseware UT2004.exe is a game, so now I get buttons 1-5 working fine. And no longer will my middle button bring up the Ogg/MP3 Player screen.

I can map 6-8 to keys, but I'd prefer to have them map to button6, button7, button8 in the ut2004.ini
Barring that at least to be able to map them to keys that aren't on the keyboard ... F13 - F24 are likely candidates...
Law is confused