I don't think that you can. Most of the F keys are already reserved for other functions that can't be overriden. I remember experimenting with OnLayoutKeystroke and these keys and found only one that didn't have a function already assigned to it...
I'm getting a lot of grief from my data entry people, I'm just going to have to tell them to suck it up, and get used to hitting "ctrl n" Thanks.
I've had success with the function keys on a wired mac keyboard F16-F19 (above the numeric keypad)
Code(Get(TriggerKeystroke)) = 63251 for F16 ... = 63254 for F19
Haven't done much experimenting to see what else works, I only needed these 4.
Unfortunately im not on a mac.