Guitar with Piano resonance

I suppose this is the best place to post this rather than an ongoing thread in the Coffee House.
 
In Dave Cousins's autobiography he briefly describes the technique used to create the guitar tone on "Down by the Sea" on the "Bursting at the Seams" album. I have always been amazed by that tone.
 
The guitar amp was placed under a grand piano and the pianos sustain pedal held down with a heavy weight so the piano strings resonated. The microphone arrangement is not mentioned. Listening to the track again now it makes sense.

I just looked up pianoverb and it would seem to be based on the same principle. I had not expected to be able to recreate that effect in software but I will certainly be trying Pianoverb now.