PSX + Free McBoot

I recently acquired a rare piece of gaming history:

Among the major design flaws, its well known that when the internal HDD goes, the console is essentially a paperweight...until recently.  A specific Free McBoot install for PSX is available - however you will need to manually direct the console to boot from the memory card.  The button you need to hold down on system startup is R1.

This will throw you into the file browser where you can then execute your .elf of choice (such as OPL).  I spent entirely too much time trying to find this info on the web - you're welcome.