The way I see it drifting between frames shouldn't affect the noise as calibration of darks and biases is done pre registration and stacking and after calibration the noise should still be uniform and random in nature.
I'm using a CCD by the way. Anyway to continue making bias and dark frames I have the camera sitting in the fridge this morning (the deltaT on my camera isn't getting down to -20C at the moment
). With any luck by this afternoon I'll have enough new bias and darks to try again.