Like I said in my thread, I had trouble finding examples for MIDI decoding but while searching found a ton of projects that send MIDI data out. Let me know if you have trouble finding what you need and I'll go back through the myriad of links I saved and post the relevant ones here for you.
I was tempted to do this myself although I couldn't figure out a way to make it programmable without connecting it to a computer. However, I only gave it a few minutes of thought since I already have a GCP. Although, I must admit, I would be kind of cool to build one and then sell the GCP to fund other projects
Have you decided how you want it to work? If you're using it only for the MP1 and don't mind having to adjust the code to make changes, it shouldn't be that difficult. Just make sure you shop around for your switches since they can get expensive and vary widely in price.