Presentation graphics in Solidworks Addin - Temporary bodies?

Hello

I am working on a C# addin and I would like to display a visualization of a non-Cartesian coordinate system  in the model view.

I thought temporary bodies would be a good mechanism to do this but it appears they can only be displayed in the context of a part/component. Is this so. 

Is there a better method that can be used to display presentation geometry in an otherwise empty assembly or subassembly?

Thank you

SolidworksApi macros