Somewhere there is an instruction on how to do this, but I can't remember where!
It is to do with setting up registrations with a dummy style. You could use a style that you never want, set all the registrations, then remove that style from the keyboard (obviously not a preset file) I recall that you could rename an existing style, then revert it's name to the original after saving all registrations. The keyboard when it cannot find the registration style does nothing and so the style does not change. I think that is how it is.
Keith