Having been on both ends of the scale - total acceptance and prohibition - at work would guess it doesn't matter much what you wear with the kilt, the kilt will be the issue if there is one.

Only suggestion I have is to wear exactly what you'd wear with pants on a casual Friday only substitute the kilt for the pants - if that works for you.

If you feel the need a tartan shirt can add to the cultural message of the kilt.

It helps if the turnout looks nice though. Check Hamish's gallery for coordination ideas. He has a lot of UKs. I have some UK's at work pics in my gallery too but don't know how helpful they'd be.

Enjoy the freedom your boss has given - it is a gift.

Ron