Why do you want them eating pellets?
Vampire Tetras are one of the most specialized freshwater piscavores. If I were you, I wouldn't even worry about getting it off of live. Teacher fish sometimes help, especially when they hit food quickly. A lot of predatory fish that are mixed with cichlids start to take whatever foods the cichlids eat. However, this can take a while and even longer with one of the most piscavorous fish in the hobby.