What about the following idea:
Everybody gets the same defined amount of fuel, like 5 % or so, but every race attendant has to choose another car, so ideally the whole LFS car range is covered.
Then, with the green light, everybody drives as fast as he can with the target to see which car covers the longest distance.
Well, I must admit, this will work once only, because then everybody knows which car is the worst gas guzzler, but after that you could still experiment with different extra weights or intake restrictions in the advantaged cars ...