The folks in 3d printing helped me out greatly with this, and I was able to mash this together today. I haven't printed or tested it yet, but it's designed to be used with the quad mag ring. I'm going to use some very thin and strong 3m adhesive tape I have to ensure it is secure to the phone, and use for a quadlock mount on the bike if it actually works.
Perhaps this niche case will be useful for someone else?