Need help with sound sculpture

[feJ]

I'm a grad student at Rutgers University, working on my Masters in Fine Arts thesis show, and would like to build a piece that is nearly fully developed, except for one key part.  I'm building a sculpture that "plays" the paint-roller texture of a wall.  A small plastic needle runs down the wall.  Attached to this needle is a contact microphone that picks up the sound from the needle, kind of like a record player. 

What I would like to do is have the signal from the needle modulate the volume of a sine tone (coming from a separate source).  I would prefer a hardware solution (ie: circuits, effects pedals, etc.) rather than a software one.  I know this could be acheived using MAX/MSP but I dont' really know the program and don't want to have a dedicated computer just for this project if I can avoid it. 

The only other idea I had was some kind of modified envelope follower that took two inputs and modulated one based on the other.  I'm totally stumped.  Any suggestions?