Could short-circuit it, connecting mobo power back to the PSU without a diode or something to stop the current.
If you cover that, might do something that would fry the card. You would have to hook that incoming power to the power phases on the card so the energy the GPU gets is clean. And they might not be able to handle the extra current.
All number of things, would be a pretty complex task. Would need something a bit more precise than a hand-held soldering iron.
If you value the card and the rig attached to it, I wouldnt try it. If not, go ahead, though I don't really see the point.