If your cuppa goes cold in the time it takes you to drink it, drink it faster. Coffee is medicinal, and you can never have enough tea.
However, with this inspiration, I can take a stab at another problem.
Why do fingers freeze when in contact with computer mice?
It seems I'm a bit late to this party, with commercial units for about $25, but it's so easy to do yourself with the seemingly endless supply of discarded mice.
With this in mind, I present my USB heated optical mouse.
Step 1: Power
If you place a hot cup of tea on a set of scales and allow it to cool, it looses about 25 watts of power by evaporation alone.
(measurable by mass of water evaporated per unit time * latent heat of vaporisation)
My soldering iron would have trouble keeping up with that.
USB specifications allow you to have 2.5 Watts total. (5V * 500mA) Feeble. However, this can get comfortably warm.
To maximise power draw without your computer making a fuss, you can place 10 ohms accross the power rails in your USB device.
Two 22 Ohm resistors in parallel should do while leaving a bit of room for the original circuit.
In this case, I need a nice distributed heat so I'm going for two 10W wire-wound resistors simply for the size. Distributing the heat means you don't melt the plastic.