How to escape square brackets in a tokenisable field

I'm trying to figure out how to put a square bracket set into a tokenisable field in such a way that it doesn't trigger the token replacement machinery, and can't see it documented anywhere. The only suggestion I've seen is to percent encode the square brackets. That isn't a solution though, because it assumes the field is destined to be streamed into a HTML output stram (and without encodingit at that - ugh). In my case, I'm trying to generate an email subject field, so *ML encodings aren't applicable.