Watermark certain pages

Watermarks can be added natively as follows : 

• To one page
• To a continuous range of pages
• To the entire PDF
• To even-numbered pages
• To odd-numbered pages

But not to specific pages.  The Acrobat UI handles page selection much like those familiar printer dialogue popups, but good luck in trying to add a watermark to pages 3, 12, 17, 21, 23, 25-29 in one go.  

Theres a thread about adding watermarks to every fixed number of pages, but the script on there didn't work - kept getting undefined errors. 

For example, using the 6-page test file attached, I'd want watermarks on pages 1,3,5,6.  In real life it'd hundreds of pages.  How do I add watermarks to a list of specified pages? 

Thanks.