You know, arson is always an option. A wedding you say? Can fit a lot of people in a church, and most of them don't have too many fire safety precautions...
You can't suffacate yourself :/ you pass out trying and then obviously can't carry on and t start breathign properly. Plus it's generally a bad idea.
It would just take some careful planning. If you were to place your head inside a bag say, and then arrange some sort of reasonably airtight seal around it that didn't require you to actually hold on or anything, that would work.