flomaster: https://www.homebrewtalk.com/f35/methods-shipping-empty-cornies-221664/ this guy seems to think that you can just ship the cornys with a sticker on them. If it would make your life easier, and if (in your opinion) you think they'd reach me just fine (minus a few bumps and bruises) I wouldn't have a problem with that at all.
I would think shrink wrapped wouldn't be a problem. You might need to make end caps out of cardboard but I've shipped quite a few things that way with no problem when I was the shipping & receiving manager at my last job. Some things like pelican cases or other types of road cases didn't even get shrink wrap. Do you have plastic strapping at your work? You could always shrink wrap them and then band them with the plastic strapping to make sure they don't come apart (which is probably the concern from UPS). I do see this listed on the UPS web site however if it helps since I would consider kegs to be "bare metal items".
Bare Metals and Other Irregularly Shaped Items
Packing
* Please tape corrugated cardboard pieces to all sharp or protruding edges for protection.
* Cover the other surfaces of the item as needed.
Labeling
* Please tape your address label securely on the flattest surface of the item that you are shipping.
* Cover the entire label with clear tape.
* Do not use "flying tags" (tags that hang from the item that you are shipping).