The other issue you will have is weight.
^^ Particularly this... It's important for the fan to be lightweight for RPM's and CFM flowrate. The fan itself effectively never sees the temperature off of the heatsink (other than transferance through exhaust, or through bearing => axel contact as rubix_1011 mentioned) though the actual benefit through either is defeated by the ~8x higher power-draw
(ex, .25A to 2A)
However, a fan modification that would help (if designed properly) is a cowling on the exhaust side to increase airflow speed.
Please, keep thinking! This world needs more thinkers and less rock-star / rapper wanna-bees.