ah i see. constraints probably will not be enough if it has to go to a game engine. But I dont know enough about animation in unity to suggest what to do on that end. to attach a simple dummy object really all you need to know is a location of a joint being updated per frame, so as long as you can access a joints location…
if the animation only being done in maya? if so you can use parent constraints, dont need additional joints. Also worth looking into Animbot if you'll be doing a lot of animations - it has some helpers for this sort of thing that is a lot less fuss compared to using native constraints.