I think the UK Workman would be just fine to wear there. I agree with getting permission on company letterhead, but I also think you'd have to become the star employee and never make a mistake as the manager will be looking for an excuse to fire you. Another thought is while I'm fine with a guy in a kilt waiting on me, many men don't understand what it's all about (their loss) and take offense. Perhaps your manager is afraid of losing business because of it, so instead of being confrontational, just ask him (after you get Corporate approval) why he doesn't want you wearing one. He may open your eyes to the bigger picture and/or you may open his to understanding you.
On a side note, last week I dreamed I got a kilt made out of pleather and on the back it had the orange Home Depot logo on it. Weird, I know.