A Mechanic in need of a Game

On a recent road trip, I came up with a mechanic (or at least the start of one) to make running a game on a long car trip viable. Since dice tend to be a pain in the car, I found myself thinking about other ways of generating numbers, and came to the (rather obvious) conclusion that there is a ready-made solution to the problem: license plates!

There are several (potential) problems here, including that different states and different countries use different formats for their plates, and the fact that it can be hard to verify if someone really did just find a plate with six nines on it. I'm still working on a solution to the first one - so far I think just reading plates until you hit the right number of digits is the way to go - but the second one suggests to me that players should be encouraged to try to slip in better numbers, and hope they don't get caught.

What I'm looking for now is a bit of a push on the theme and general idea of the game. I think a backstabbing feel would encourage the "number fudging" part, and probably something playing off the tight quarters and lack of mobility - a prison, maybe?

Let's throw some ideas around...