Have X number of roles, predetermined in random order (i.e. balanced but random). First however many needed to start = "Original Townsfolk" and have balance there. When Original Townsfolk are taken, game starts.
As players sign up, become "Clueless Newcomers". Theyre out of their first day and night phase and have no powers. On next phase, gain npredetermined role and start participating.
Lynches and NKs aren't required, so days/nights could pass with nothing. And let's keep days at 48 hours, nights at 24?
As players die, their roles die, but they can choose new players after 2 days/nights pass. So, X dies, waits 2 days, and re-enters as Y, Clueless Newcomer on first day.
Game ends when either all Wolves are dead, or Town remaining (including Newcomers) = Wolves remaining (including Newcomers). Could end up at some points with only Town or only Wolves until someone joins/revives, but unlikely.
Not sure if I could run b/c I have no ide aabout balance for WW games, but I could try.
Example:
Spoiler
Show
Original Townsfolk: Players 1-15
Clueless Newcomers: Players 16-40 (or something)
Players starts signing up as spots 1-15, which are randomized and balanced. Initial Wolves know each other; Newcomer wolves don't, though some are mason wolves so do. Likewise, there are masons for villagers, both initial and newcomer.
After first 15 spots, next people take Newcomer spots (anywhere from 16-40, predetermined roles). Dead people can revive as these spots as well, so could have many roles if you want. So don't need 40 people; probably only 15-20 if need be.
So I take spot 12, which is a Seer. First day goes with lynch and second I scry but am killed. After startup but before Day 1, cd4 joins as spot 23, which is a wolf (non-mason) and enters as a Clueless Newcomer. Can't participate in votes Day/Night 2 and doesn't know role. Finds out role on Day 3 and votes for lynch/wolf kill. I revive as spot 30 on day 4 which is a villager. Day 4 comes and goes without my help, and I learn of identity for Day 5.
Alternatively, Clueless Newcomers can participate in lynch votes.
As for waht roles there are, it's up to narrator, but pretty much any role would work. Seers, masons, disguisers, baners (day as well?) are a must, and NK roles or some special roles can work as well. Other game mechanics could be added if wanted.