There's a reason they make mini-quiches for appetizers and not mini-racks of ribs.
Although if you could figure out how to make a mini-rack of ribs, I'd be all for that.
I just have so many issues with the concept. One, you should only do this if both options are equal- in popularity, portion size, deliciousness...really, everything. Even then, you run the risk of people not wanting, or not being ABLE, to eat one of the choices.
If you're charging 100 dollars a plate, just go ahead and let your guests choose. This isn't a case of "be happy for the free food", it's "Here you go, egg and mushroom pie". For the price, everyone should be happy with the food.
Now. If you pay your 100 dollars and know full well you might end up with a mushroom pie, but you decide to show up anyway, take the pie like a manly man, or trade with a table mate.