EHX "Memory Boy" feedback control mod, anyone?

[Johnny85]

Hi

I just got an Electroharmonix Memory Boy.  Analogue delay, square/saw modulation, chorus, vibrato, the whole shebang, for 70 quid new. Not bad!

http://www.ehx.com/products/memory-boy1

Problem is, unless I put up with very few repeats, the feedback/self-oscillation seems to always be on the verge of destroying my amp; since I sold my beloved motorcycle to pay for this Boogie, I really don't want it to be killed by an unruly delay pedal! 

I have heard that the Deluxe Memory Boy has expression pedal control over the feedback - my simple MB only has pedal control over the modulation or the delay time.  I would love to mod the pedal so that I can use an expression pedal (which I'd have to buy) to control the feedback, since I don't want to have to keep kneeling down on stage or in the rehearsal room to tweak the feedback pot by hand to save the amps...

Does anyone know how this modification is/might be done?  I can't find a schematic and the inside of the MB is daunting to a noob like me...