Unfortunatly you are supposed to drink the shakes within about 15mins of making them so that you have all the vits and mins that are in them.
Do you not have a shaker, where you can shake it up by hand when you're at work? Or is it possible to contact your cdc tonight explain the situation and see if you can pop round and get some tetra etc.
The only other option is to have your first one, just before you walk out the door and then the next shake as you walk through the door after work? I know its hard that way, but if you keep glugging water all day you should be ok, depending on your type of work and how many hours you are there i guess.
At the end of the day if you have a shake that has been made up a while it might not taste too nice, but would be better than buying a sandwich!
Sorry I have not really been very helpful!
Good luck x x x