I can't do this try myself because I programmed my VU+ remote volume k-eys to control my TV and not the OBH volume, but in OBH many k_eys can be assigned to the function you like going in
MENU/Setup/User Interface/Button setup
Have you tried this way? Go there and press V+ or V- and then choose the function left/right.
Actually, some k_eys are not recognised by the Button Setup and so you cannot assign them to any function (and I fear V+/V- are among these...). But you can try, at least.
If not possible this way, you can choose many other k_eys for the left/right function, without having to edit keymap.xml