Rigify: How do I parent a custom control bone to rigify's eye controller in the metarig

Hey,

I am using rigify to rig the character for my recent project. Rigify face rig does a solid job, but to bring the rig even further I do want to add some custom controllers to make it even better. E.g. I would like to add two additional circular controllers to control the size of my eyes’ pupil and iris.

I know how to add additional custom bones/controllers to the metarig so they get transferred to the final rig when “generating rig” or “overwriting rig” using rigify. Now here comes the problem: Since my iris and pupil controllers should always stay in front of the eyes. As an animator I would expect these controller to move with my eye target controller, the one sitting right in front of the eyes to control the view direction. Since this particular controller is built by rigify only after one hits “generate rig” or “overwrite rig” button I simply cannot parent my custom bones in the metarig to a desired bone.

So how do I parent my custom contorl bones to the eyes controller built by rigify?

The only advice I got on StackExchagne was to highjack the rigify source code, but to be honest, I was hoping for a better and more intuitive solution.

You can find the sStackExchange thread over here:
https://blender.stackexchange.com/questions/237557/rigify-how-do-i-add-another-controller-as-a-child-of-the-common-eye-controller

I hope you guys understand the problem and have some smart solution to it :)! Looking forward to your answers and ideas. Thanks in advance!