I'm curious, why would you want this? Why not just turn down the master volume? I can understand an intentional mismatch for certain tube amps so you can drive the output stage harder and get a bit more drive for the amount of volume (and apparently Jerry Garcia did this with his McIntosh MC2300, which, despite being a solid state amp, has a tube style output with an output transformer).
@agedhorse you are 1.5 billion times smrtr (and more elegant) than myself, why do we this kind of feature?