There's a certain amount of flexibility I think, as far as how people deal with the hunger and there are definitely ways to sate it that won't muss up the limits of the plot, but yeah. I should also mention (& will in my email!) that Daybreakers vamps can eat solid food, so if they want to stuff themselves with whatever's at hand that's fine. It might make them feel less physically hungry for a little while, but without blood they will start to feel sick after a bit. XD