Roland V-Piano - How can I,...?

I love the V-Piano - the best digital piano out there. Here's the scenario: I've used the GM2 sounds in the piano for writing charts and basic sequencing with a laptop - works great. Since I can access those sounds via the MIDI in, and the V-Piano sends MIDI via MIDI out, is there a way to layer some of the internal GM2 stuff with the V-Piano sounds for live gigs? I've worked with it a bit and get some success just using a MIDI cable from the MIDI out to the in and making sure the channels are set as to not cause a loop. I thought of using a MIDI fader box of some sort to have some control, but I wondered if there was some secret handshake or something to make it easier?