What a cool problem to have!
But really, you need to figure out how hard you plan to run on the Poker run. If you don't care whether you run hard or not, it sounds like a great opportunity to fill the boat up with Miller girls.
If you plan to run hard, it doesn't make sense to expect newbies to be comfortable or to know how to act in a boat at speed. And a PR lasts a long time if somebody isn't really liking it.
I'd suggest that all people who end up in the boat on the PR have at least a couple of hours in the boat prior to the event. And give them an opportunity to experience how you plan to run the boat in similar water conditions.
Be sure to keep posting pictures of the "candidates".