I might give it a shot. Sgt. S. has always been larger-than-life and I think it'd be a really cool thing to have.
I haven't made a single con', and I don't know if I'll ever make time to make it out to one, even though Hascon has me really curious. I even used to live in San Diego but was always deployed when the famous SDCC was held.
I used their site to find Sienna Miller successfully, I also tried lady Jaye Adriene Palicki and never heard from her. One other one I tried was a more major star and never heard back from them either. It is a crap shoot but all it will cost you is a stamp.
You could contact him direct on twitter, he might answer you, he replied to a few posts today, it is his birthday. he called a Joefan who praised him a Maggot. Classic.