Discharge curve of a LiPo battery
Whilst I cannot provide you directly with a "generic" forumula that will solve your answer I'd suggest you perform an experiment like the one completed in this youtube video. You'll need to insulate the battery in a fixed environment at a temperature you are keen to analyse.

http://www.youtube.com/watch?v=ln8Mlz4NsW8

With the raw data you will be able to derive an equation.
I highly suspect that you'll find huge variances based on the number of charges the LIPO has gone through and I suspect your results will vary based on LIPO age as well.

http://chemistry.about.com/od/howthingsworkfaqs/f/coldbattery.htm