John Fass Morton

From Fettipedia

Actor - The Empire Strikes Back (Boba Fett, in Cloud City outside Han Solo's torture chamber)

While Jeremy Bulloch was tired up in previous acting arrangements for a while, John -- a stand-in actor who played Dack, Luke Skywalker's snowspeeder co-pilot -- stepped in for the "he's no good to me dead" sequence with Darth Vader.