I don't race USAC (non-sanctioned league), so I don't have a horse in this race, but...
I would waive the 1 day license fee if you attend a training course, and discount the race fee for those on an annual license that haven't already taken the course. USAC can reimburse the race promoter for the lost income, because with training it's more likely you'll have a greater number of return customers. Hook them any way you can, and financial incentive to take a training course is a powerful motivator.
The training doesn't have to be cosmic to be effective. Basic stuff like cornering in a group and general pace-line guidelines can go a long way. There's going to be crashes, no matter what you do. People do stupid stuff when they're gassed. All you can do is mitigate that somewhat by opening their eyes to what many of us take for granted as common knowledge.