Graham has said something here that I think might help your situation. It will also be something you can do together. This is a big plus for most relationships. Scotish Country Dancing is a great ice breaker. Here you will be around other men who wear kilts as it were an everyday thing and their spouses, make no big deal about it,... only to comment on the tartan or lack of (which is sometimes the case when I wear a contemporary kilt).
By keeping it a secret, in my opinion, is giving it a "Closet" conotation and methinks that is not what you would like your wife to think about you. Enough of the angst, life is too short...believe in yourself....acknowledge your wife...do something special together... if it's in a kilt all the better. Check the obituaries if your not listed, go out and enjoy the day.
Cheers
Robert