As a licensed carrier of a firearm, you do not have any 'cover'. If you are concerned about co-workers discovering you are carrying while employed, you can do one of four things :
1.) Let the folks you ride with know you have a CC permit. See what they say and go to option 1 or 2.
2.) Resign your position, if it is against company policy and you don't feel your co-workers will let it be, or
3.) Do not carry co-workers in your private vehicle, say your insurance does not cover such things and you'll drive alone from now on.
4.) Do not carry while on the clock.