I had a similar thing happen where I work.
Find a sponsor (someone in upper management who is friendly to the idea of charging at work) or speak with the manager who gave you permission in the first place, and then with that person, attempt to address their concerns through the proper channels (typically HR). They are usually:
1) Safety. This can be resolved with a $15 GFCI and a $15 'while in use' box. If maintenance can't do it, a licensed contractor probably would for less than $100. Offer to pay for it.
2) Cost. This can be resolved by offering to pay for whatever electricity you use. Speak with someone from AP and ask them what they are paying per kWh for electricity, then offer to connect a Kill-a-Watt, and pay per kWh. It will be pennies per day.
3) Preferential treatment. This happens all the time in workplaces. If they truly value you as an employee, they won't make a big deal about this. Also, offering to pay for the plug and electricity will eliminate this concern entirely.