I also think it is possible to do.
I read this article https://learnopengl.com/Advanced-Lighting/SSAO
It gives a pretty good explanation on how ssao works.
I think the fragment shader in coin3d is the place to implement this. But foes coin3d use deferred rendering? So that we have the needed information available?
And the openinventor mentor states that a fragment shader replaces a lot of built in functionality like texture rendering and stuff. So this has to be reimplemented in the shader i think