[joe_the_user]

A practical implementation of this could be to choose N people at random and send them a letter or text message instructing them to pick e.g. the (modulo) 5th person from their contacts list whose name begins with R.

I'm sorry but in modern America, you can count on the average person screaming bloody murder when confronted with a scheme like that. No one likes to be part of someone else's mathematical model but a random electrician or hairdresser is toss that away or maybe put out an angry tweet that will get more leverage than this idea.