Chris F,
Is it safe to assume that you didn't read about what I did for my wife's family in Colombia? It is along those lines as what your talking about, and perfectly legal. It was a blessing of the rings, but no vows of any kind took place...so it's not a "marriage" or "wedding". No one is man or wife yet and it's definitely not going to jeopardize a fiance visa , but her family and friends get a chance to celebrate and give congratulations for the wedding they will miss in America. (Two different immigration lawyers, with thousands of visas under their belts, already told me it isn't visa fraud.)
Thats about the only thing they can do without commiting fraud and getting in trouble, because they can't get married before she leaves.
What city is she in?