As the title states I want to cut a shape to a variable depth.  I have included a simplified photo of what Im essentially trying to accomplish.

So essentially i want to cut the space out between the rectangle and circle (on front plane) to a depth governed by the half circle sketched on the top plane. I understand I could do a rotational cut and then build the pin boss back up, but the actual part is more complicated than the part seen above and would avoid removing the details already created.

I have also included the part.