Both those ideas seem like a solid flame, but I think he's going for more of little pops or bursts of flame? The thought had occured to me to just use a bic lighter, the kind you use to light the bar-b-q. Since when you pull the trigger it makes a small electric spark, it yould avoid having to use a flint, and you could use a tube to pipe the fuel into the exhaust tip. This would take some creative mounting of the car, some creative wiring, but conceivably you could push a button and make little flames come out the tailpipe.
In any case, this seems like a good way to set your model, workbench, and house on fire. As well as you. I don't think I'd ever do this, though it is a fun little pipe dream.
Pun intended.