Junk Mail postage paid envelopes

In this article http://www.vertical-visions.com/_temp/postagepaid/index2.html, a guy explains how to use postage paid envelopes to send up to 72lb in weight which will be charged to the junk mail sender.
His solution is just to put any old junk in there however perhaps a better option would be to send junk that you would normally have to pay someone to dispose of like old computer equipment (not hazardous waste like Asbestos though).