100-400L with new x2 converter

I've been trying out my 100-400L (at 400mm) with a new 2x Canon converter and I'm amazed at how shallow the DOF is. Granted its mid winter with dull grey skys but at around 10mts I'm getting fractions of inches shooting the birds at our garden feeders. It means that focusing is critical and even then I struggle to get both the bird and the feeder in focus together.

It means that the background is well out of focus which is nice.

AF would have been nice, but I am resigned to its loss. Probably spoilt because my previous 1.4x Kenko let me AF.

Just wondering. Would taping the pins allow me to fool the AF into working?

I know that this will create other issues, but I'm exploring the possibilities.

I think you are going beyond what this lens is designed to do. It woks OK with a 1.4, not good, just OK, but a 2X is just too much and the loss of image quality with a 2X would be worse then a cropped 1.4image. To answer your original question, there is no way to "trick" this lens to auto focus with a 2X TC.
I would add that the depth of field at 800mm at a distance of about ten feet on your camera is about two inches. That along with a dark viewfinder caused by the loss of two stops of light would make focusing very difficult. You could try using live view and brightening up the viewfinder but I still think you would find the end result to be not worth the effort.