The 'which key starts the car' is a good, reliable promotion. Sure,
it's been done nearly to death, but if it hasn't been done in YOUR
market, it's new to your listeners. If it HAS been done in your
market previously, you should go a different route.
What about renting several (6-10) of those Nascar racing arcade
games (the big ones that you sit in & can be networked together)
and having your qualifiers race each other to win the car? Single
elimination, winner from each preliminary 'heat' comes back to race
the other heat winners in the final feature race...winner of that
one gets the car. Fun for the qualifiers, and entertains anyone
else who happens to be gathered around.
Or how about the very same idea, but racing go-carts at a local
go-cart track?
You could team up with a sports bar & have your qualifiers race
slot cars. If your manger's cheap (and what mananger isn't?) you
might even trade with a toy store for the race track.
Here's one that takes speed out of the equation. Remember the
old Brady Bunch episode where Greg & Marcia drive an obstacle
course to see who's the best driver? Borrow some cones & barrels
from your local road department & set up an obstacle course in a
sponsors parking lot. Put raw eggs on top of the cones, of course.
Qualifier who navigates the obstacle course destroying the fewest
eggs wins.
Just some idea-starters. Maybe one of 'em will get your creative
juices flowing.