Clip one end of the jumper cables to the battery and short the other end across a small chunk of metal until it gets hot enough to ignite paper (or just spark them onto some torn up paper), add whatever else you have to build it up, add paper soaked in engine oil until that ignites, and then feed it with oil-soaked fabric and eventually shreds of tire until those burn readily, and then the whole tire (deflated first of course)

Just what I would try, not really sure if you could get it hot enough. Maybe a lithium battery would add enough oomph?

I thought about using the upholstery or plastic panels from the dash etc. but that's probably all flame retardant on any modern car.