I'm not entirely for sure, but there ought to be an option to allow you to transpose the keyboard up to a whole octave without having to do the tuning manually (unless your tuning and your guitar player's are different), so you ought to be able to tell it to transpose down just a step in the same fashion. i know that works with most other roland boards (atleast their digital pianos), but i can't swear on it with the gw-7.

i think i remember seeing a gw-7 at my shop. if it's still there later today i'll check it out.