As far as I can tell (and I've been through it pretty thoroughly) you cannot. But if you are handy with doing your own homebrew stuff, you might use Limor's design as a good starting point.
You can probably use part of her firmware code to do the MIDI reception, and part of her circuit design for the MIDI circuit and power supply. You will need to add some D/A converters to the circuit to make it do what you want, and you will need to modify the firmware at a minimum. Also the app that runs on the computer will not do what you want it to do, so you may have to write your own version of that. But all the schematics and source code are available for you to work from. Good luck!
P.S., Figuring out voice assignment is non-trival. Do you do assign a note to the least-recently-used voice, the most-recently-used voice, the closest voice (based on its last note), or the furthest voice? It will operate a lot differently depending on the algorithm if you have "glide" on.