I'm not to fond of heating springs to lower a car, although it has been done quite a bit. I disassembled my struts and cut them with a cut off wheel on my angle grinder. If your bottom spring perch is the style that cups the spring then it is easy to cut them, however if your spring is a full circle on the bottom and that is what holds the spring onto the perch, then you only option might be to heat them. Although I would probably use the clamps first for a Proof Of Concept before taking the dive off the deep end
I lowered mine 1.5" and have a slightly positive rake, can't say it helped the mpg pursuit by any amount I could measure. Even at only 1.5" below stock I have bottomed hard enough to hit my header on the ground and destroy my o2 sensor, but that was a pretty radical gas station apron.