Over the last few weeks I've been working on a prototype for an Ergocine-type shoulder rig for my a7s. Here's where I am with it at the moment:
It was a long process in researching the best mounting options, cheapest rails and clamps, and figuring out a good form for the wooden counterweight. I'm still not quite there yet. I will continue to fine-tune the shape of the wood until it is comfortable and practical. I plan on creating a space for an external battery within the wood form. Here's a photo from one of the intermediate steps:
I've used the mount on a few jobs so far and It has served me well. It even provoked conversation from subjects about the nature of the rig, allowing them to feel more comfortable and natural in front of the camera. Once I finalize the form of the rig I'll create a new one with nicer wood. Since I'm already taking more than a few notes from Ergocine, I'll probably end up using some sort of walnut.