I flew in a contest last weekend in cool temperatures, so I blenderm taped off all of the air intake except the air that is ducted to the motor. I've left the tape on, and I'll only take it off if I fly in warm weather again this year (not a guarantee in Saskatchewan).

So, altering air ducting is one way. The other is to insulate the packs with something like a cloth or rag. Consider doing a glow-style full throttle run on the ground before take-off, too ;>