What might be an interesting "hack" implementation would be to make the play rule drop-down list include (at least) 3 strategies: always gain gold, always draw, and always remodel. Then if you have multiple buy rules for Governor, the play rules specify that you use the play rule for the Governor with the highest buy priority.
That way, users can do something like have a "buy rule" at the top that says something like "buy governor if [in action phase] and [gold in hand] and [at least 3 governors in deck], which will allow the governor to be played for the remodel in this situation, and default to some other play rule if the conditions aren't met (by having a different rule selected for the place where you actually buy governors).