In the W7 clone, it is pins 1 and 20 with a 20k pot that controls current from a front panel trimmer.
I tried this on an old PJ, to no avail. It uses pin 20 ( on the wire header) as an inverter on led drive signal, and pin 1 is gnd on both.
Pin 2 on the main chip seems to be involved somewhere, and R23 grounds that ... maybe to set current max. not sure at all. It makes sense that there is a resistor somewhere that controls the current max, and thats the one I would play with first... but I'm not that interested in the PJ boards any more, and you seem to have the skills to take this further.
Let others know how you get on with it.
Be careful to turn inverter off first before unplugging grid, or the back elf in the torrioid may kill the fets.
...........oztules