They can be modified to work with a C-mount. Now that being said, it's not a simple thing. The physical modification is pretty simple. The modification necessary to get the driver hooked up and working is a different story. I have yet to get one working but I have no doubt I will very soon. I will show you a picture of the modification
I ended up placing a blank PCB over the top of that and attached the driver to that PCB. Only issue was, my driver was putting out over 3A and it kept frying the C-mount.
Once you modify it for c-mount though there is no going back to 5.6mm.