It appears that your boss' "policy" has nothing to do with finding the answer you are seeking.
The "agreement" (contract) he has with FedEx will either say that the FedEx Code of Conduct will apply to contract drivers or there will be no mention of it. If the first case you are contractually prohibitted and would endanger your boss' contract if you were caught. If the second case you and your boss need to work out the public perception issue - especially as it relates to delivery sites that are posted. (The customer, your boss and FedEx will not like it if you are delaying deliveries to take off/put on your handgun.)
Have you considered a breacher bar? http://www.countycomm.com/eodrtool.html You can refine the edge and tip to be sharper, and making a kydex sheath is iterally child's play with a heat gun and an old pillow or folded towel. Better than your 4" knife because delivery drivers need something like that all the time.