I e-mailed a con asking something similar. The organizer told me he gets hundreds of such requests and dealing with something like that would be an enormous amount of work.

If I were you I would call or email the comic con and ask if it is possible for this to happen. Alot of times they will sell items from celebs that are appearing.

If I mail a check payable to whatever star I would like to sign for me, plus a photo (I know for sure they are going to be there, just not what day :() do you think if I wrote 'hold and forward to... ----' they would pass it on if I included an SASE? Has anyone tried this before?

I'm willing to take a gamble on it. I'd really like it to work out. :( But I figured I'd ask beforehand, I'm not sure if this is a ridiculous idea or not...