For building up spent brake drums I've been curious about trying a thermal spraying process aka "flamespray" or "plasma coating". I've seen various mention of people using this to build up spent wear surfaces before.
These guys even mention using it on clutch plates and brake drums. Some of the coatings can be finish ground after application as well. Looks very promising to me:
Hmmmmmm. My only concern would be that the heat might separate the cast-in drum from the outer aluminum casting due to the difference in coefficient of thermal expansion of the two materials. The flame spray process is much lower temp than welding though, so maybe it wouldn't be a problem. Who wants to be the guinea pig?