If people drift around the course and start causing a mess, DQ them. I just did a 45 lap run and the tires are OK but get worse when you slide the rear. By drifting the tires will get eaten up. Now the first corner is tricky because you are coming into the lefthander under braking and you will sometimes loose the rear end. I hope you won't be anal about it lizard but I understand why you are trying to enforce it.
If the odd person slides their car, you should ignore it. If a person blatantly goes sideways a few laps in a row, give them a warning, and if they repeat, kick them.