Lo-Chlor has a product called Leak Sealer. It is not for vinyl pools but from what I read on their website it seems to be for plaster or fiberglass pools. Since Lo-Chlor is a Horner company and a sister company to Autopilot and AquaCal perhaps PoolSean knows a bit more about it. Perhaps a PM to him might be in order?

http://www.lo-chlor.com/pool_chemicals/leak_sealer.php