Yep, just keep a mouse button pressed while cold booting - the default is the LMB, the exact one depends on the bootloader installed in the Algor. Check the Luciferin docs.
The button has to be held down during the entire boot process. My OS4 partition isn't my default, so even after I select it from the Early Startup menu I have to continue to hold it down or the Algor FlashROM will activate. When rebooting OS4, I have to hold down the button or the Algor FlashROM will activate. It's a bit of a hassle, but I don't know any other way around it.
Poseidon can be safely started from the OS4 startup-sequence by adding the line ENVARC:PsdStackLoader
I put it right before C:USBCtrl START.