Hack: Set the "Ready Message" on HP printers to INSERT COIN

[nickb]

http://kovaya.com/miscellany/2007/10/insert-coin.html

[cstejerean]

This is a clever hack often used by university students on unprotected printers. It's much cooler if you combine it with another option that disables all the buttons on the printer.

[extantproject]

This is about ten years old:

http://www.irongeek.com/downloads/hpnt.c