I wouldn't think you'd have to fear losing your job over this unless you became uncivil while meeting with the board. You have a legitimate request, and a kilt is a mans garment. In fact a kilt is probably the most versitile mens garment out there. A kilt can be worn super casual, to extremely formal, and everything in between.

I'd suggest keeping the tone of your presentation cool and professional. Keep all your points professional and on topic. I'd think it would help out to point out inconsistencies in the dress code too. When a decision is finally agreed upon get it in writing. Probably, should you lose, the decision which now have in writing could prove usefull in either exposing your employer as culturally/ethnically insensitive, or be used to force female employees back into skirts. I add this because they will either try to say it's not culturally significant, or it's not a male garment.

Also, keep an eye open for employees who violate the dress code for ethnic or religious reasons. Some one in another department might have been allowed to wear a turban in violation of a no hats policy for ethnic reasons.This would be hypocritical.

Lastly, remind the board that you are really only looking to wear the kilt on Fridays, when the dress code is relaxed anyhow.

I almost forgot, don't forget, you could notify the press.