hi, what I was just thinking of here, not checked in regulations though...
I actually think it is possible to drive in races with a lower weight than the minimum needed in F1. See you get fuel for say 20 laps, this is when the car is checked before the race. Suppose this is 60 kg above the minimum weight. Now say there is actually 80 liters in the car, that would mean that at the end of your stint, you drive 20 kg under the minimum
Cool isn't it