This is a common problem when you enter ketosis, so first of all take that as a good sign!
Secondly, there's not much you can do I'm afraid. I've read a few posts where people are taking their toothbrushes to work, others state that keeping mouthwash in your handbag and there's also the option of mouth freshener spray (but there's no confirmation if these are allowed, so if you use these go easy).
Drinking plenty of water can help but not eliminate the problem.
Don't let it bother you too much, just pick one of the above and carry it in your handbag.
Just think: the things we do to get slim will be well worth it in the end!!!
Keep up the good work!
Best of luck