The AutoCAD Product Feedback Contact Us web form received a submission the other day. The actual product team members monitor this email alias and reply.
"I would like you to improve the XCLIP command so that you have an option to suppress the display of Xref not only outside of the defined boundary but also inside of it, sort of being able "invert" the clipping area."
I sent a personal response back within minutes explaining:
"Thank you for using the AutoCAD Feedback form. AutoCAD 2008 has added a
new XCLIP Invert option. You can try the feature in the AutoCAD 2008
trial download at http://www.autodesk.com/autocad-trial."
New Xclip Invert option