will this short-circuit anything?

[rommie]

I have only one pci-e slot in my machine that I need to use. The problem is, I have a huge-*** cpu fan that means any card longer than a couple of inches is going to have the back of its pcb/possibly solder joints touching against the heatsink. Having a card like this directly against the heatsink would short something out, right? Could I do something like put one of those rubber sheets you use to grip jars and things with, or some thin plastic, between the pcb and heatsink and solve the problem that way?

 

[Bobnova]

Shorting anything on a GPU will cause issues at best and fires at worst.
Can you rotate the CPU cooler 90* to give yourself some clearance?

You could put something on the back of the card to protect it, I don't really recommend it though.

 

[Conumdrum]

Yea, you can use something, even a thin piece of cardboard like from any food box like a cereal box would work fine.

Not the best solution, BN is correct, fix the main problem. If you can't, cardboard.