Adding thickness to a sculpted single side plan in Zbrush

Three65

I am working in Zbrush with a single sided plane that I have added a substance height map to the texture to displace the plane. I am now trying to add some thickness to the backfaces of the plane. I have been looking around and have found how to add thickness to a thin object with the Zmodeler brush. However since this has been divide up to around 1 Mil polys and displaced with the Deformation Inflate tool I am not sure that method will word. Does anyone know of a way to add some thickness to a single sided plane that has been sculpted on? 

Octo

Extract can add thickness. Same with the panel tools.

musashidan

There is also the old-school morph trick to get thickness.

Open the Morph palette>store morph target>move your tool a distance equal to the thickness you want>creatediff mesh(from same morph palette

Biomag

...and you also have doublesided panel loops as option.