Heating the spring is the worst idea you have, what others have told you is correct. With heat you will ruin the rate AND have no control over the amount of drop, heat one side just a few seconds more and then that side ends up lower than the other, once it starts to move it don't stop until it cools enough. Cut the spring, thinner isolator, or replace the spring. I have also cut springs with no bad affects on ride quality, it will only be noticable if you cut more than 1 coil off.
Heating the spring is never acceptable, and will lead to fatigue and broken springs since you are changing the heat treat of the spring at the point you heat it.
Heating is definately "ghetto".