I'd seen a book on wedding practices and customs that said if desired in appropriate cases, a memorial prayer ("El/Kel Malei Rachamim") could be said under the chuppah, e.g. a bride/groom who lost a parent fairly young, and would like to have their memory honored (assuming it's not too painful).
This book tended towards Hassidic customs, so I don't know if this custom is limited to the Hassidic world; I haven't seen it at any weddings, but that doesn't prove anything. Has anyone else heard of or seen this practice? (Or a Sefardi Azkara for that matter, I suppose?)