Starting fluid is about all I can think of to use when its this cold outside. Something a bit more flammable than the crap gas that is available nowadays.
I haven't put the bike down for the winter yet but was trying to get out and start it every couple of days or so and run it to operating temp. At one point I hadn't done so in about two weeks, coupled with the temperature drop (low 30's), the battery allowed for just a couple of revolutions and that was it. I threw it on the solar charger for a couple of hours, blew some fluid down the airbox lid and it started. Reluctantly, but it started.
I keep the solar charger on it for now and I think after this week, it'll be going to bed till spring. The new fuels have less energy than the non-ethanol based ones coupled with the cold weather not allowing the fuel to atomise as readily equals no starts (for carbed bikes anyway). I already account for mine running like poo below 55*.
-Randy