"passenger" mode for boats, where they can be freely moved using leads

No idea how to properly word this, but I've been seeing community members make designs for monorails and things with the new sulfur cube. The only problem being they require a pig with saddle in a boat, which just looks kind of strange. This is done as a workaround to the logic of "If a player is in a boat, give that player full control of the boat." I would suggest the ability to give boats some sort of "passenger" mode, which would provide them with the ability to be moved more freely by leashed mobs, such as the sulfur cube. This could also be useful to create "chains" of boats, that players are able to all sit in in one line, and be moved about by the leading player.