I learned this one a couple of years ago from a student during an
etching class I was teaching.
Copy your designs onto a glossy magazine page (free) using a toner
copier - not inkjet. Make sure you feed the finished edge into the
copier so it grabs and does not jam. Transfer the image to metal with
an iron, hot plate or what ever method you use for PNP Blue. When
transfer is done, quench in cold water and rub the paper away. The
toner will remain. The toner is the etching resist, even with PNP
Blue, the blue film is just a transfer film for the toner. The glossy
magazine surface acts as a transfer film and works perfectly.
And again its free