when I did group b'day cakes for an office I usually would try new techniques or designs. Being a small work place there usually were no more than 4-5 people celebrating that month so I always piped the names on.
Any chance they are all women? Do something ultra feminine; for men use circles in a combination of blue, green, brown &/or tan along the lines of this:
http://cakecentral.com/gallery/1351608/generic-mans-birthday
Depending on how many the cake needs to serve, try a small tiered - topsy-turvey is always fun to try.
What kind of work place is it? Can you do something related to the type of work?
Hope these suggestion help you come up with something
http://cakecentral.com/gallery/2104049/an-aldonska-knockoff
http://cakecentral.com/gallery/1356978/football-player
http://cakecentral.com/gallery/1333233/hot-dog-birthday http://cakecentral.com/gallery/1332863/chocolate-birthday-sheettime
http://cakecentral.com/gallery/1317617/stars-streamers
http://cakecentral.com/gallery/1300407/
http://cakecentral.com/gallery/1289892/generic-sheet-idea
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