In GRID, you need to turn on the 900 degree rotation of the G25 on the PS3, then use the saturation in game to reduce it to the degrees you want. Lower saturation == less degrees of turn. I'm guessing the same trick will work in F1 2010.
There is a button combo to do it on PS3 (I don't have access to the PS3 atm or I'd check it for you) it is something like holding SELECT+R2+R3 as you start the game. Both green lights should come on if it works. You have to do this every time you start the game.
30% saturation should give you 270 degrees.