Excellent question. One way to deal with it is for all the relevant agents to agree on a bet that's actually specified... that is, instead of betting that "AspiringKnitter is/isn't the same person as WillNewsome," bet that "two verifiably different people will present themselves to a trusted third party identifying as WillNewsome and AspiringKnitter" and agree on a mechanism of verifying their difference (e.g., Skype).

You're of course right that these are two different questions, and the latter doesn't prove the former, but if y'all agree to bet on the latter then the former becomes irrelevant. It would be silly of anyone to agree to the latter if their goal was to establish the former, but my guess is that isn't actually the goal of anyone involved.

Just in case this matters, I don't actually care. For all I know, you and shokwave are the same person; it really doesn't affect my life in any way. This is the Internet, if I'm not willing to take people's personas at face value, then I do best not to engage with them at all.