I settled on this as the final form. The clip is printed in two pieces and then just snapped together. I used some adhesive backed foam to add some grip and give. There are a variety of line weights that might be used when fishing, so I needed a flexible clip that could grab a variety of diameters. The clip is also rounded to eliminate any stress on the line during the process. If you hook a 180lb tuna, the last thing you want is a kink or minor imperfection in your leader, it will snap and everyone will be very sad.  The clip must not introduce any imperfections into the fishing line.

Here is the final clip wired up and attached to a DJI Phantom 4: