I don't have my Cube in hand yet, but the base fan is one of the first things I'm planning on doing.
I have a box of dead video cards, some of which have heatsink fans built in. I might see if I can come up with some sort of fan and heatsink arrangement that will fit the GeForce and work within the confines of the Cube core....assuming I can get it to help, I'd think that would solve the heat issues.