Extrude profile to surface in a different part

[dcook.188104]

Is there any way to extrude a 2D profile in one part "up to" a surface of another, separate part?

If you look at the attached picture, when I extrude the square profile "to" the cylinder, it creates a cylindrical profile on the end of the square extrusion. Is there any way to do this across two parts? i.e. if I wanted the cylinder and the square bar in the attached photo to be two separate part files, one cylinder and one square bar with a cylindrical cut out at the end of it.

I know for this example I could just project geometry, but I'm trying to do something that has a 3D profile (not just a 2D shape extruded in a third dimension), so I cannot just project geometry.

[Bunny]

You can do this with a multi-body part.

[JD Mather]

Or in assembly edit the first part in context of the assembly.
Copy Object the Surface of the second part into the first part.
You can now Extrude up to the surface.
Turn the visibility of the surface off.