Its a semi cheap solution but do the bypass idea (I did it with my skylark til I could replace the heater core, God, that was tons easier than my blazer is going to be) but I also hit my local auto store and bought a portable 12v heater to put on my dash to defrost and keep the cabin warm. You just have to remember to unplug it when you get out. That will keep ya warm while you're driving at least until spring when you can yank out that heater core (this is what i'm doing tomorrow because i just replaced my thermostat last month and I stopped getting heat sat night)