I remembered that they sold these big battery emergency jump start kits at auto stores. They were fairly straightfoward, when your battery is dead you just plug these into your cigarette lighter socket and it allows you to start the car...
So why not simply kill the alternator and strap one of these on there, and you can power all the electrial systems of your car from one of these things, and then charge it when you get home...
here is an example of what I'm talking about
:
car battery starter - Google Product Search