Two choices - either use a smaller pinion - or get a fan.
My suggestion -
Novak fan:
http://www3.towerhobbies.com/cgi-bin...?&I=LXKKN0&P=7
Screw it directly into the ESC and if you have an extra channel on your receiver, plug it directly into the + and ground and you'll be set to go.
Also - depending on the location of you ESC mount cut some holes in your body to encourage some air-flow over the ESC when running.