To my amazement, I found print-o-matic which does exactly what I needed! ...and it's developed by the awesome developers behind collapse-o-matic! All I had to do was pop my collapsible content in a div and use print-o-matic to print the content in the div. No fuss, no muss! Shortcodes make it a snap. Batteries not included.
Thank you Baden & twinpictures!