Learn about timing.
I never shoot wedding even with digital, but if i have to use film then i have to learn how to load film faster, i know getting more backs or inserts will help, but i try not to do weddings where i can't do things quickly and properly, i can load film in less than 1 minute [could be 30-50sec], i think 1 minute loading/unloading the film will not kill weddings photoshoot, even with digital i may miss the moments, so what a big deal if you miss something during 1 minute of replacing the film? I will use my Mamiya 7II because it can do 120/220 easily without replacing the back[it doesn't have changeable back except for 35mm pano].