How about a prequal for each race? I'm sure not everybody will be able to show up at every race, that has been the case in every league I've seen. So, if someone doesn't show up for whatever reason, next one on the hotlaps chart could take his place. This makes things complicated for organisers but I think its worth it. Otherwise we won't be having full grids of 23 people and those who dropped out before the season would be frustrated not to be able to race when there's a space for them after all.
So a system with joining each race on the website would be needed, and 23 with best hl times will be in the race, but with a possibility to pull back from next race before some deadline? Don't know how much difficult that would be to make.