Sometime, I have geometry that is hidden from view... behind part of a model etc, and I want to project that geometry onto the sketch plane in order to create some new feature. For example, imagine a part with hollow tubes inside of it that might be used for cooling or to deliver a cooling fluid. Now, say I want to create an orifice that matches the exact inner profile.

In other software, I could use "Project Geometry" command and select "hidden" geometry, and it would become projected onto the sketch (normal to the sketch).

I found this video on: Surface Area Projection

You have to be able to "select edges" and then you can "Convert Entities" and the projected lines etc will go onto the sketch:

Like this:

My problem is that hidden geometry that is Inside of a Part, doesn't seem to be able to be selected.

A simple example: is a hollow cylinder in the center of a cube.

I tried to select the surface and convert it using "Convert Entities" but I am unable to select the geometry inside the cube:

My question is basically, how can I project the cylinder, that is hidden, onto the sketch plane?