? Octaver that trims guitar tone & vol automatically

[LP Hovercraft]

Have any of you tried a resistor/filter network to ground that backs off on one's guitar volume and treble automatically at the input stage of, say, a Blue Box or Octavia or Green Ringer or Uglyface (switchable), Scrambler etc... so that you only have to switch to your bridge pickup when kicking on your favorite octaving device as a convenient live performance measure?  This is assuming that any volume lost could be boosted at the output stage of "x" device.  It would be cool to reproduce this with a trimpot/trimcap network so it could be tuned to one's ideal setup for flexibility.  I wouldn't see any problems with the trimpot, but trim caps are usually in low values and less easily obtainable.  If you have tried this, could any of you let me know if there are any magic values to this (single coil or humbucker)?