if you're not afraid of putting in a small transformer and another valve socket, you could add another output stage - single ended, class A using an ECC81, around 1w.
tap the signal from one of the EL34 grids and feed it to the 1w output stage, could even have a master volume in there too. just add a switch to lift the cathodes on the EL34s to mute the normal part of the amp.
If you're local to Frank at JPF, he'll know how to do this - give him a shout.