Ollivanders has been done before already, so try and do something original to be different.
Maybe have a replica of the ring in one of the storefront windows, maybe hanging on a necklace around Hermione's Yule Ball dress, while you guys stand and take pics in front of that window, an employee dressed up as a wizard walks by and you ask a question to them regarding the ring in the window. The wizard gives a spiel(that you right) that is the magical love ring made to bring the love and souls of 2 people together, blah blah..you can elaborate on that, after the spiel the wizard takes out a wand, casts a spell and the ring "magically" shows up in your hand, tells you that you are worthy of that ring and at the moment you do the proposal.
Granted it won't be in front of a crowd completely trained on you as in Ollivanders and there may be people walking by that will stop and see, but you won't be announcing it to the world to stare if you don't want that.