Of course, if this is something you tend to do regularly, an easy solution would be to save the town after evicting everyone manually, essentially creating a "master save file". The best idea would be to move that file to a different folder so it could be copied and pasted back into the saves folder the next time you start anew. That way, you'd only have to do it once.
This is something I've considered doing myself, just to get a random group of townies. I never actually did it, because it just seemed like a whole lot of work lol.