i've seen people weld the bearings up inside the cassette body carrier hub thingy (to use the technical term) to make it fixed... xcutterx did it to a wheel. some track guys get road carbon discs and do this to them for the track. i've also seem a transvestite get beat up by a cop.

edit: i left this window open too long while typing a pm and didn't see fixinskitchin's post. brazing would be way easier... i've still seen a transvestite get beat up by a cop though.