If you mean using XIM NEXUS with the new XIM device, it will be possible as far as I know. But I don't how well stacking gyro input from NEXUS with mouse input would be as they both do the same thing. Everyone who use devices like Sony Nav or a PS or Xbox controller with XIM APEX use the left-stick instead of WASD movement rather than right-stick as well as a mouse.
Maybe you mean assigning NEXUS Motion Aim to left-stick movement rather than right-stick aim (if that's possible, I've never tried). If you have both a NEXUS and an APEX, you could probably test this now by plugging the NEXUS adapter into APEX's USB hub and using NEXUS controller instead of the keyboard.