I like @KMatle
's approach but need to add a step:
SUB McGyver(Action asString)
Run after person driving off in your car
This is something that I've dreamed of.
Nice cozy un-icicled car with clear windows to get into on the way to work.
I was thinking Arduino powered blowtorch but turning the car on and have it run a while is a lot less explosive.
Realistically we are talking nothing less than total control of the car's electronics...
and remembering to leave it out of gear
As cars become more electronic this might be something that you could sell, though at the moment asking people to solder bits all over the place might not work.
I expect the latest in vorshprung deutsch teknik might involve an onboard alarm clock allowing one to do this without unlocking the car but only gazzillionaires can afford one.
A lower-tech solution might be that if you can park your car in the driveway then stick a small fan heater in the back that you can turn on from in the house, but again coffee starved early morningers might forget to unplug it and drive off with sparks and wires trailing.
The answer to this is to feed the wire through the drivers door so when you go to get in, in your morning funk you will think 'what's this wire?' and remember to unplug it, as you have to climb over it to get into the car.
I can confirm though that shutting the wire in the door to a small fan heater doesn't damage the wire.
Not the door to the fan heater, the door to the car duh