Foundations below grade

[Bionical]

I want to show the foundation in dotted lines in a layout sheet.

I do not want to trace the foundation out and change the lines to dotted and then move the viewport up to hide the foundation, because if I make a change to the plan, the change is not shown.

I am not making the elevation into a cad detail and then sending it to the sheet. I like to keep my elevations real time incase changes are made.
(which they always seem to do)

Why can't elevations show hidden lines below the terrain?

Thank you for any help

Brian