how to 'rig' an expression pedal for the Mutron Bi-Phase ???

[Derringer]

I can make a few bucks if I can successfully fab an expression pedal for a guy I know who has a Mutron Bi-Phase.

I'm hoping that I can just get away with routing the 5-pin midi cable into a Crybaby shell and solder in the proper wires to the pot.

there's a schem here
http://m.bareille.free.fr/biphase/the_vintage.htm

and the schem showing the rate pot itself is here
http://m.bareille.free.fr/biphase/vintage/mutron_biphase_sch1.gif

from this page
http://archive.ampage.org/threads/0/fxgen/001395/Re_Anybody_seen_the_sweep_pedal-1.html
I see that "Of the 5 pins on the foot pedal jack, they consist of in no particular order,  
+15vdc  
Channel A enable  
Channel B Enable  
one side of the reostat  
other side of reostat (I think I spelt that right)  

Shorting the +15 to Channel A or B turns each channel on induvidualy or simultaneously and I just connecting a pot across the remaining two pins will adjust the rate. "

but then when I look at pics from here
http://www.....org/viewtopic.php?f=19&t=3847&p=41737&hilit=biphase#p41737



I see someone wired three and not just two connections for a pot (at least that's what I'm assuming)

any idea what i should do?
The pot in the wah shell that I have is 100K and seems to be linear

[Derringer]