I think you do not have anything else to do than applying 2 methods:
1-specify that you offer a 12 USD Gift card to the PSAs who participated in the Eager Zebra games as often as the 12$ Gift Card permits
2- specify that you offer a 12$ Gift card for the ones who are willing to use it entirely for the Eager Zebra games exclusively that month and that, if they qualify as an EA for that month, the following month you will support, each of them, with 10 TC, too.