hmm, if your handy with filler and paint, if its a pretty standard, non metalic colour the way i always do it put a screw in the centre of the dent, doesnt need screwing all the way in, just a bit, then get the other end of a claw hammer and pull it. sand some of the paint off, then rust treat and filler the small hole and get your spray out! may be a bit severe but sounds like the only way.