Ha ha
My initial experiments were not great but I haven't given up yet.
The main problem remains though - PR8 uses so much processing time that it's difficult to effectively decouple the editor from the playback engine in a way that you can consequentially decouple the audio refresh from it's 60hz/VBLANK base.
I did get it working whereby the 'clock' was determined by hitting a button on pad 2 so I know that that method would effectively work. It has limited use though, admittedly.