What do you mean by 'viewport clipping planes'?
I figured out this workaround..
* read pointcloud in file
* set density and pointcloud properties
* open new DWG
* xref inported DWG with the data
* determine position of the sections
* xclipframe = 2
* make sectioons using xclip copies
* draw the 2D/3D polylines
Any other good routine or feedback
http://youtu.be/_rVePwKOdYE