Check these out!
This is exactly the kind of thing I had in mind for Stickvise - mod and hack to make custom fixtures for holding PCBs. These are a cool set of jaws by @bfesser that not only hold two RasPi zeros, but you can flip them around and hold any size PCB. There is actually a dual and a single jaw set available. Enjoy pics below, if interested in 3d printing these, head over to thingiverse to download.