Shortcut for pick focus point for focus panel

Is there a shortcut that can be HELD, to TEMPORARILY pick focus point for the focus panel.
I know that "F" is the default shortcut for the focus point picker, but is there one for temporarily switching to this tool only while the shortcut keys are held?

The equivalent of what I'm looking for like we can hold the spacebar for the hand tool, or option+spacebar for the loupe.

Anyone know how to do this - and also where these shortcuts can be found? I'm sure there may be other useful ones I'm not aware of to temporarily use certain functions.

Thanks,
Clark