I would suggest a DNA test, but I fear that it would turn into another out of control PSA/DNA thread!
I can't believe eBay won't remove the negative. I might almost be tempted to have them leave it with the verbiage as is and post a simple "Unbelievable!" type of response to it. I think folks will see your spotless record for the last 12 months coupled with the user's newbie status, and quickly figure out that eBay will allow any clown into their community...