Ok, I have a THD Hotplate (16ohm) that I've used live before just to bump down the volume in clubs with my JCM 900 SLX. This unit has a line level out. Could this be used for our propose?
Since this no dummy load, you still need to connect your cab. Hard to say if it changes the sound. Perhaps give it a try and turn the loading to zero so that the full signal is passed to the cab.