I don’t use IndigoRT so I can’t advise you on its use. At the very least you could turn on Shadows in SketchUp so you would have the sun.
I use Kerkythea and the SU2KT extension which has tools for adding lights.
One thing I often do when I want to show divisions between faces that are otherwise flush is combine rendered images from KT with hidden line exports from SU. For example, here’s a render from KT. The lights provide the shading to show the form.
And this is the hidden line export.
And, when they are combined:
The black lines aren’t very realistic but it’s a simple, fast procedure and it gets the point across.