Just a comment, but the BMW clubs and Porsche clubs both allow co-drivers. They do charge a few bucks for the privilege (like 10%). The idea is that you've paid for the track, and you can use it however you like. Clearly, if you do this, each person gets less run time.
Not sure why it's harder to administer- Red Lotus #7 is in run group 2. Don't care who is driving it. I wasn't trying to have two people pay - I'd pay the full amount, just when I got there, someone else could drive in some of the sessions. I agree having actual pro-rated payments would be a mess.
Anyway, appreciate you setting it all up, and however you want to run it is cool. I was just hoping to bring my dad along and let him drive once or twice.