This is actually a pretty common scam on eBay/PayPal. They only require tracking to verify a return, and you can literally put anything in that box and still get a refund. If you're lucky, eBay will eat the refund charge themselves and not ding your account for having a case opened against you. All you can do is to be thorough and detailed in everything you do.
That said, sign the dick head up for any number of different and embarrassing mail services. Gay sex toy catalogues, free magazine trials, hate group newsletters, etc. etc. Just make sure to cover your tracks.