I just picked up a Kenton USB host for this reason. Aside from finding an oplab, or icontrolmidi box, the Kenton is your best option. My prior solution was using an iPad with camera kit or irig midi. This works great as you can run it usb and not interfere with your midi routing. On the iPad I use midi studio pro and midi studio lite. With both running I can have a split key controlling active channel for 2 octaves, and the other instance controlling 2 specific channels that I always want access to (track 1-2 typically).