John - I feel your pain but hope I don't repeat it as I was also just thinking about that option on my (to-be-picked-up-this-week) HCH. I briefly looked through the PDF install manual and I remember it said to remove the rad drain plug but that really isn't necessary. I added a water temp gauge on my previous car and all it took was to remove a plug in the engine block and to replace it with the thermocouple insert for the water temp gauge. Sure it is safest and most wise to drain all the coolant and replace it but I'm confident that you can do this install just by removing the coolant plug and replacing it with the block heater insert. One end of the plug goes to the battery and the other to a three-prong plug. I don't see why removing the hard-to-reach drain plug is required (recommended maybe but not required). Any thoughts?