I found these and am thinking about trying them out. My 2002 base is pushing 140,000 miles. My bump stops are rotted away and I think the upper bearings are shot. Going to replace those items first and maybe use these replacement inserts later. I see this post is a little old but figured I'd share this anyway.
Porsche 996 Boxster Strut Insert Shock Absorber: Steering and Suspension & Shock Absorbers and Struts