Still casual, but slightly dressier than beach attire, is the linen suit option. Perfect for daytime events, the light-colored linen suit is sure to make its wearer achieve that elegant-but-not-trying-too-hard look.
Of course, linen wrinkles easily, so caution your groomsmen ahead of time to be careful about lounging pre-ceremony. Be sure to have an iron on hand in case last minute touch-ups are necessary. Also, appoint a qualified ironer to tackle the task. Chances are if you let your future brother-in-law do it himself, he'll end up with a giant burn mark smack in the middle of his thigh. That will make for hilarious (but not so lovely) photos!