There is a drill that Ron Clifton does at his clinics
(http://www.bowl4fun.com/ if you are interested in having Ron put on a clinic in your center). He gets permission before doing this from the center management, then he puts a chair over the gutter cap and places a mop or broom handle so it hangs across the lane about 18 to 24 inches past the foul line. At this point he has the bowler follow through and try to reach out and knock the mop handle off the chair with their fingers.

This does two things; it builds a solid follow through and second it develops extension through the target.