... errrmmm.. something like this ..???

I'm no techie, so you'd need to check the 'specs' to confirm if it'd work well enough with mic levels
and if it'd be too noisy without balanced DI..

http://www.artecsound.com/effect/vpl-1.htm


"Artec Volume Pedal VPL-1
The VPL-1 Artec Volume Pedal features minimum and maximum volume controls and 2 outputs (1 fixed gain and 1 adjustable gain)."

approx £40 before haggling.. + a few quid for a couple of XLR to jack converters..