Eh, they could make a flexible one like they did with sli connectors, of course more heavy duty due to the current but still in the same ballpark. I don't know enough about the workings of Pcie slots, so I don't know if such a thing would cause a short. Though I'm fairly certain there'd be some sort of on board circut solution that could be intiegrated into the video card to alievate that risk.
Not that a lot of people would be running them in sli. Though I know some people do, to make a quad but that being the case for the most part they are running massive extreme mobo's that have an access of slots, generally designed to deal with triple sli anyway, so there should be a couple of spare pciex1 or similar they could plug into.
Wonder if something like this could be done in such a way that it could use pcie or just a normal pci to function. (Again, pulling this out of my arse and I'll be the first one to state my lack of knowledge as to how the pcie and pci slots work from a technical standpoint)
If that was the case even on my teeny board it would be possible to run 2x 590's (if designed in said manner) That are not underclocked due to power constraints as quad sli.