Ok to put this in perspective my 8800GTS/512 idles around 50C and peeks in COD4 at 65-66C. This is with the GTS dual slot cooler. Your GT, even with the nice Gigabyte cooler is TOTALLY within acceptible temp levels. Don't worry about it at all.
As Jtt283 said, who says it's a fan plug. Don't even try plugging something into it. You don't want to be wrong and put a resistance on something that shouldn't have it or create a draw in current. Just leave it alone. I'm sure Gigabyte tests the crap out of their cards in all climates to make sure it will work. If you want to exhaust heat, get a good rear case fan. Leave it alone and get back to playing COD4. If you aren't lv 55 and have all 5 gold weapons and all challenges complete, you have more things to worry about than card temps.
I play as Mike Rowe, you better watch out on those servers.