Add a volume remote?

Check out Placette's passive volume controls. They come in two models, one with one input as you describe and one with 3 inputs. They appear for sale used with some regularity - $500 for single  and up to $1000 for triple. An excellent product.

 If you are going to use a passive attenuator, remote or otherwise, you need to be certain that there is no impedance mismatch between the device putting signal into the volume control and the device being driven by the output of the volume control. That is sometimes a complex problem. For that reason, you might be better off with an active device. 

Khozmo, with the shunt and series resistor upgrades.  Send him the input impedance of your amplifier, and he'll recommend the correct resistance for the build.  

This unit emphatically replaced a Slagle autoformer volume control, which is no slouch itself.