What a bummer! My mom tells me that she keeps a small amount of powdered milk on hand for emergencies like this. Not anything you would want to drink (well at least I wouldn't as I don't like milk in any form) but not too noticable in a recipe. Also - if she doens't have the powdered milk, then she keeps a small amount of reg. milk in the freezer. Like freeze some in ice cube trays, then when they're frozen dump some cubes into a zip lock. Again, you probably wouldn't want to drink it but it will work if you really, really *need* it!!!
Better luck next time!
Tracy