And you do that, how? How do you keep them from coming to any church they wish, or masquerading as "good" Catholics? Believe me, they know where the enabling "priests" are, and that's where they go. An official excommunication from the Church isn't going to keep them from using Catholic appearance to manipulate the electorate.
If they are thrown out of the Church, they can't say they are Catholic in any way, shape or form. Place any priest who helps them under interdict, and excommunicate them too if they don't cease and desist.