I would do something similar to what MikeC has done then. Have your fan by the side of the cards to circulate some air between the two graphics cards. Secure the fan any way you can. It might even be a good idea to mod your case to have the fan mounted in the side cover to suck even cooler air in. That would work even better. That's how I've got mine setup up but the Stacker cases make it very easy to do so..
What case have you got?