actually all you need to do is buy a used second hand H1 or H2 on Ebay or wherever.
and the H1 or H2 does not even have to work...
I use a H4X with a P30+ and it works fine. The H4X is an excellent camera.
Initially there were some issues with IQ backs but those apparently have been sorted out and addressed through firmware updates. It is said to be stable now.
The H4X does not work with Leaf Aptus II backs and most likely will never work with Leaf Aptus II backs:
http://forum.getdpi.com/forum/gear-fs-wtb/35978-fs-new-h4x.htmlMamiyaLeaf does not list the H4X as a supported camera for the new Credo backs so I would first thoroughly test that combo before going that route...