http://www.freestompboxes.org/download/ ... &mode=viewthe stoner mode just requires a single wire from Q5's source to a switch and then through a 22u electro cap to ground - will give a big gain boost and more dirt.
I'm not sure whether the stones mode would give a gain boost to the OG SFT, or whether it gives a bright boost, or even gain reduction, but the input stage is slightly different in your original, so the stones mode would require some tinkering - add 10k resistor between the first two JFETs (Q1 drain-Q2 source), replace the 1u cap but connected to to the Q1 drain instead of Q1 source -still at Q1 gate at the other leg. The stones mode (another, opposite wired pole of a dpdt) connects a 4n7 cap and 470k resistor in series between Q1 gate and drain.
Check out the schematics out at freestompboxes - Trace your original (page 5 of the thread) and compare to the V2 schematic with the switch on page 15: There seems to be few changes (I assume those two scheme are correct).
http://www.freestompboxes.org/viewtopic ... &start=280