Can I recruit random passers-by?

Yes, you absolutely can - first, select one of your colonists, turn them into a militia member (R), and then right-click on the wanderer and select "arrest [name]".

You have to have a prison set up - an enclosed room with a bed marked for prisoner use is all that you need - and then wait for your colonist to bring them to that room. (Don't forget to take your colonist off of militia mode when the person is in the room!)

Once they're there, you can do a bunch of fun things like executing them or trying to recruit them. Make sure that you're having friendly chats with them (click on them and select the prisoner tab) and their loyalty will go through the roof.

Once they're loyal, you should then enable the option for your warden to try to recruit them (also on the prisoner tab).

Enjoy your increased population, however keep in mind that this will automatically lower your standing with the persons faction!
Which means instead of visitors, you'll have a lot of angry townsfolk coming to attack you.

This Hospitality Mod might be what you are looking for: https://ludeon.com/forums/index.php?topic=11444.0