Ask the players where their characters get their blood from. Really make them think about it, especially if the PC in question has no business hanging around fingering hoboes or picking up prostitutes. Do they have a trusted servant who bares vein for them twice a week (paid overtime for the pleasure, of course)? How does the servant feel about this? Above all, what would happen if that safety net of regular, planned, safe feeding was taken away? This is always a good plot to break out if the PCs don’t create one for themselves, or in the lull while you frantically work out how the hell the local Tremere are going to react to having their chantry filled with lawn ornaments or what the Toreador primogen thinks about having her childe’s illegal blood doll left in her conservatory with a note saying “people who live in glass houses can’t throw stones”.