Scott Adams once tried to prove on The Dilbert Blog that nobody has free will. He did so by challenging anyone with free will to copy and paste a statement to the contrary as their response, and predicted all valid responses (ie you will not do so, you will do so but with additions, you will rant or you will copy the statement verbatim, thereby stating the opposite of your point).
There's something wrong with that argument, though, because it can be used to prove exactly the opposite point, too. That is, I know you have free will, but I command you to copy and paste this statement verbatim: "I have free will". If you don't, you've proved my point, because you've demonstrated your free will in disobeying me. If you do it, you've denied what you say. If you add to it, you've also demonstrated free will by choosing what to add to the statement.
So I don't think that experiment is valid either way.
Mokalus of Borg
PS - This was a few years ago.
PPS - I stopped reading The Dilbert Blog around that time.