The managers where I work recently started bringing a cake to work once a month in honour of everyone's celebrations. It didn't matter whether it was a personal celebration (birthday, wedding, new baby, new house, etc.) or a professional one (achieving an accreditation or certification, or presenting at a conference) the cake was to celebrate everything.
You have to remember that the goal with these "celebrations" is that you are trying to build and maintain a positive morale among your staff. If you take away something that they are accustomed to doing, how does it benefit morale? Will it make your job of morale building easier or not?
Understand that your beliefs regarding not observing the kuffar birthdays if it is the company's directive could put you in legal jeopardy for discriminating against persons on the basis of religion.
If you are serious about your beliefs to the point that you cannot stomach the thought of offending Allah by celebrating with the kuffar, you really would be better off seeking employment with a Muslim-only company.