I'm surprised I remembered it. I had a copy of that PDF on a network HDD which failed a few weeks back but vaguely recalled it had several unconventional but simple methods for getting the most out of minimal hardware. I have a new, bigger NAS drive but had not grabbed a copy of the PDF until your post jogged my synapses.

The Atmel AVR ATTiny12 allows you to use MCLR as an open drain output but its pinout is different.