How about this. If you accept money, you're a "Pro". If you don't you are not, even if you compete in a "pro" event. (Same as golf)
This way if you are a guy/gal just into the bottom end of the open you can ski a pro event, but declare yourself as an amateur. Same for talented juniors who want to try some pro events. Only the top 1-3 places normally make more than their entry fee back anyway. Those top 3 skiers aren't the ones this is aimed at anyway...
I understand that this doesn't go with language of the rule John quotes, but it seems like a simple fix.