Since it isn't an official relationship that is recognized by the Tower, I don't see why there would be any official rules/regulations other than the guidelines provided in the Library. I say you just do it, but that's just my opinion. :tug
Syera Sedai - Since it isn't an official thing, you don't need to notify anyone. You just prepare the ceremony yourself and get enough people to participate. Vendri and I did our First Sibling ceremony at a local Tower event. ^^