I am thinking you will have to go with an inertia rest such as the trap door or something on those lines. I don' t think you will have much luck with one that uses a string to the cable. With that bow, anybody can shoot it at different drawlengths. And if your wife has a longer draw than your boy, she could yank the string out or the rest won' t be up all the way for her.

Hope somebody else can help you more than me.