If you make the view a xref, or self Xref, then the xclip can be any shape, circle, star, etc. I use a polyline all the time to so I can easily modify the xclip.
Roger Donaldson AIA CSI CDT NCARB abUsing Datacad since 1986, ver 23.00.02.15 (SE) http://www.RogerDonaldsonArchitect.com
The "regular" 3D Clip Cubes are not able to have polyline fence boundaries. Symbol Clips and X-Clips can have polyline fence boundaries, so I typically make a self-reference on a new layer, apply the X-Clip, and save it as a GTV.