Open up the side of the case, leave it open. Point a 8 - 10 inch Tabletop fan at the GPU.
May not be ideal, but I'm thinking it will cool better than the passive cooler.
Which you'll end up doing the same thing with.
I've got the ATI 2600 with the passive cooler which works fine as long as I have a fan blowing on it.
Wife brings home cheap round 7 to 8" round tabletop fans. They work great for cooling. 110v ac powered so no drain on the PC power supply. Low speed for winter cooler temps, high for summer.