I am trying to create a sketch for a support rib. To do this, I've created a reference plane that intersects a body. See screenshot below.

I want to create a sketch on the plane (Plane5) such that one of the sketch lines lies along the intersection of the reference plane and the body (red line in image above). Is there an easy way to do this? I haven't had any luck using sketch constraints. Running SW 2016 x64. Thanks in advance.