If you're gelled up and nowhere close to a warm place to drag your equipment to, you can do this, but it's a pretty desperate measure. I can vouch that it works, so you know I have been desperate. A fire extinguisher is handy to have around for this.
Start a charcoal fire (about 5 lbs should do) in a tub, bucket, pail, hibachi, whatever you have, then build a windbreak around the gelled unit out of cardboard, corrugated tin, again from whatever McGiver-like materials you have available. Block off as many heat-leaking orifices as practical.
Once the windbreak is in place and the fire is basically glowing coals, shove the fire container under the vehicle under the area where it will do the most good and least harm.
Give it 15-30 minutes. If it isn't reduced to a smouldering pile of junk metal, you should be able to get it going for long enough to get it inside someplace warm enough to drain the fuel and replace it with #1 or some blend.
It's a relatively high-risk operation (although I have done this several times with no bad results), so your desire to have the piece of equipment running has to overpower your common sense which says, "Hey, the risk/reward ratio is very high here."
