I was thinking about this when you posted elsewhere.. I can only think of the digital system speedway sells for $100 I think which they say is designed for. other than that I'm clueless as far as what will work from the aftermarket..

BUT.... what about wiring the std flasher to the signal side of a basic relay? that would provide enough resistance to trigger them I belive, and you may have room for a couple extra relays in your fuse box