Thanks, but no thanks? Wedding edition

I got a peek of my brother's day-of schedule for his wedding, and, apparently, I have the oh-so-important task of manning the guest book. For the entirety of the cocktail hour.

I'm not close with my brother and he didn't even ask him to do this himself. Is there a way to politely decline this? I'll be traveling across the country to attend, and I really much prefer to do so as a guest instead of being relegated to a corner with a job that even the ladies of Sex and the City know is bullshit.