Nintendo had a deal with someone (att?) that all their free wifi hotspots would work as street pass relays. The way this worked under the hood is that your 3ds would see a wifi network named attwifi and then check the mac address of the ap, then it would report to Nintendo backend "hey, I just passed near mac xx:xx:xx:xx:xx:xx". Then Nintendo would note that down and also make it so the previous 3ds who visited that spot is now a street pass hit on your 3ds.

So, you would setup openwrt to broadcast a network named attwifi and make it switch every minute to a random mac from a list shared by everyone else doing this and you had yourself a guaranteed 10 hits a day (10 being the artificial limit Nintendo imposed).

An actual mobile app that worked like StreetPass that broadcast your Fediverse address via Bluetooth would be fun, except that it would hardly ever find anyone unless you are at a conference.