A half of a cap-full of stove alcohol in the boot and a flick of the lighter is a glorious thing on a cold morning. I let the flame go for a few seconds, blow it out, and cram my feet in there. Feels really, really nice.
I don't like boots in my hammock. The only exception being the Ridgerunner and its saddlebags. Alas, I can't imagine them doing much for the boots being cold in the morning.