Some people like to use the mouse more, others like to use the keyboard more. Some people want to use both simultaneously. It sounds like he wants a hotkey to bring up the palette of firemodes for the left hand weapon, and optionally another for the right hand. Meanwhile he can keep his mouse cursor pointed at his target. I think this is a good idea, as it cuts down on wasted mouse movement - especially since mousing down to click the 'fire' button tends to cause your view to scroll away from the target. As well, this would help those have Carpal Tunnel conditions by reducing the amount of movement needed to play. This is only one [well, two] of many places where it might be nice to have a hotkey, if there was a hook to hang a key on.