If you want the section to be LIVE, then this is not possible as walls have the same settings for section and plan. I keep sections live and don't like to have to rely on 2D fill overlays outlined below.
To keep everything live, I change the background fill of the existing wall composite to gray. This way you see the structural composition of the wall, but the gray background identifies it as an existing wall.
Non-live/automatic options:
You could set the wall to show as you want in plan then overlay fills in the section window.
Conversely you could set the wall to show as you want in section and overlay the plan view with a fill.
Another option is to set the wall to show as you want in plan, then change your section status to DRAFTING. Drag a copy of the section a set distance away. This various elements can of this copy can be changed without affecting the model.
Erika
Architect, Consultant
MacBook Pro Retina, 15-inch Yosemite 2.8 GHz Intel Core i7 16 GB 1600 MHz DDR3
Mac OSX 10.11.1
AC5-18
Onuma System
"Implementing Successful Building Information Modeling"