Incentivizing CS Pool for client event participation

Hello all,
We have recently made the move to having a shared pool of CSMs for our low touch mid market clients.  Every year we throw a big client appreciation event and party.

In the past, we would have a contest and give prizes to the CSMs who had the most clients from their portfolios register for/ attend our event.  However this year, we have CSMs without portfolios and we are unsure how to motivate or incentivize them.  We have thought of maybe having it be a team or regional award.

Any other ideas or experience with this sort of situation?

Thanks in advance!
Celine