If it's an assembled coil over/Spring for an FJ and you're just going to add a top out spacer, there's no need use this method. If you're changing springs around or using a preload spacer then the no compressor method is best.
yeah, I've done it a few times. Just do the normal procedure to remove the OEM springs, then remove the top hats and bolt on the spacers and reinstall, then put the new springs on.