I have actually lucked out where I have worked...birthdays are handled in a structured by membership only club. Not everyone has joined this club due to how it is handled so I don't stand out at all.
As to cards, I have just signed them because no one offers the card to the few JWs that have worked with me.
The schools I went to did not have birthday parties because some children weren't being invited. I suppose it bad enough to choose not to participate but to have others not invite you would be worse sitting in the room while treats were served to the others. The few times I was in a school that had parties, the teacher would save a cupcake for me for the next day. That seemed fair to me.
(Interestingly, I did not celebrate Valentine's day but many times received more valentines than non-JWs did...that was sad...that ended too when it was perceived as a popularity contest that was based on the economic situation of the pupil.)