That sounds like a good plan, I myself play hands free a lot with the guitar… like this: https://www.youtube.com/watch?v=ZR4IGVjaJyw
The first thing you will need is a good neck brace, and I recommend this one: http://www.jimdunlop.com/product/harp-handle it is the most adjustable one on the market, allowing you to get the harmonica in the right place for playing comfortably.
The sound box created by your hands (sometimes call cupping) will be missing, however it’s not really needed when you are playing acoustically, especially if you have a nice throat vibrato happening.
Knowing your plan, I’d suggest practicing the new techniques by hand, and then when they are happening comfortably put the harmonica in the brace and play the same things. You’ll find a slight adjustment is needed going from the hands to the holder, but this would be the way to do it. Learning everything in the holder first would be quite difficult.
I hope that helps get you going mate!
… and if anyone else has some ‘hands free’ stories or questions, please keep em coming on this thread! 🙂