One trick to help even without external heating pads is to over-wrap the abdomen and the head. The body will try to maintain these parts of your body in a very narrow temperature range to maintain proper organ function, and if they start to overheat the body compensates by sending more blood flow to your extremities (hands, feet) so they can act like radiators to dispel the excess heat. The increased blood flow to the extremities will take body heat to them as well.
That one trick is pretty limited though. Tried it for a bit last fall since I was too lazy to plug in the heated gloves. With a textile jacket, liner, heated vest + scooter (much better frontal wind protection than any bike) at up to 60km/h commute, it wasn't too uncomfortable on the gloved hands at 10C. Under that, forget it, fingers start cold burning on a 30 minute route with lots of stop-lights.