Adding Expression to Small Stone

[gurutzeta]

I have recently built a Small stone using tonepad's schem and it sounds great, but I was thinking of adding some kind of expression pedal to it. I built a simple circuit using a LED,  LDR and a volume pedal to control the value of the 1Meg Range pot and it did work, but it was not what I was looking for. I wonder if it would make more sense to disconnect the LFO and make it so that the LFO signal comes form the movement of the expression pedal, so that you create the LFO by moving up and down the expression pedal. Does this make any sense at all? have any of you done this? How does the expression pedal in the UniVibe work?

Thanks