How to do it properly:
Choose a list of victims in advance, and mug each of them once and only once - if and only if you honestly feel that they would pay up if asked. (If you feel they wouldn't, it might be amusing to send them an email describing the chance they missed.) Don't publish the list; each individual mugging must come as a surprise to the muggee. Afterwards the statistics of die rolls will prove or disprove your honesty, and the statistics of responses will prove or disprove the honesty of victims (or maybe your inadequacy as an Omega).
I'm going to test just how much the people here are committed to paying a Counterfactual Mugger, by playing Omega.
I'm going to roll a die. If it doesn't come up 5 or 6, I'm going to ask Eliezer Yudkowsky to reply to this article with the comment "I am a poopy head." If I roll a 5 or 6, I'm going to donate $20 to SIAI if I predict that Eliezer Yudkowsky will post the above comment.
Because Eliezer has indicated that he would pay up when counterfactually mugged, I do predict that, if I roll a 5 or 6, he'll respond.
::rolls die::
Darn it! It's a 5. Well, I'm a man of my word, so...
::donates::
Um, let's try that again. (At least I've proven my honesty!)
::rolls die::
Okay, this time it's a 1.
So, Eliezer, will you post a comment admitting that you're a poopy head?