Afaik all 2D views defined in the Revit project file are automatically translated and included in the Forge output. Have you looked at the LmvNav sample, for instance?
It displays both 2D and 3D views.
Note the list of available 2D views in the Secondary View dropdown:
It even links the elements in the two views so that anything selected in one is highlighted in the other:
You could check from where it gets the 2D streams. The source is on GitHub:
I think you select whether you want a 2D or a 3D stream when you supply it to the viewer.
Read more here: Source link