I think Big Mikey is on the right track. Though the conversation I'd start would go something like this:
"Darling, it would mean so much to me if I could have the honor of being your escort to a special event or dinner at a location of your choosing if I could wear my kilt. I am so proud of you and so proud of my heritage, and I want to honor both by looking my absolute best with what I have. Would you share this dream with me?"
I think you also need to be able to understand and echo back to her any reservations she may have. Once you understand those, you should do your best to try to allay any concerns, and if that's still a challenge, then fall back on the trust thing. If her objection is along the lines of she thinks it's weird, then request her support in letting you be weird, because you see it differently, but you respect one another's perspective.
If you are successful, be sure to recognize her in a way that will mean a lot to her. In fact, even if you get as far as an open-ended conversation on the matter, you should still go the extra mile to do something she would value but wouldn't necessarily expect.
Give it a go, and let us know how it ends up.
At any moment you must be prepared to give up who you are today for who you could become tomorrow.