Lelouch is going to have all the feelings during this event, between Euphie's curse reactivating, C.C. kissing him, and his own doomed inhibitions-lowered!pining. Geass hijinx will just be a bonus. (And if you wanted to get in on that, NOW WOULD BE THE TIME, since a fully-powered geass isn't really subject to willpower checks.)
I would also love to have him get, like, bitten, but I know Yuuki's keepin that in the family (so to speak). But I think if nothing else, it's a good opportunity for him to learn Zero and/or Yuuki are vampires, if they're going to be less inclined to hide their sexy</b> bloody fun times?