Hi Kathy,
I was trying on dresses & asked the consultant the same thing-- she also recommended baby powder but didn't specifically say "cake it on". I've heard many times that if you are getting really hot to go to a sink & run cold water over your wrists & forearms if possible. That is supposed to cool your body down quickly-- you could just sneak into the bathroom for a make-up "touch up" & a "cool down" for you.
Also, there are some stronger anti-persperants out there-- one is over-the-counter called drysol. You apply it at night and can use it on your underarms, feet, & hands I think. There is also a prescription anti-persperant but I don't know the name of it.
I'll just keep my fingers crossed for a gentle breeze for your wedding day!