Personally i would get a replacement fan blade! Even if you could disable the one fan, it would be detrimental to the cooling of the card.
I will do it eventually but i dont have time atm. The noise just drives me crazy
In the mean time, i would hold off using it too much as the uneven, out of balance running of the fan, MAY do damage to the motor, and the cooling efficiency of the fan will now be reduced!