I was taking another look at Judson Brewer's research (showing that meditation changes the default mode network, decreasing it's activity). A number of his subjects have reported on the "feedback" he was experimenting with for the condition of no-self or non-symbolic consciousness. I came across the Go Blue project whose ultimate goal would be to create a low cost neurofeedback device to help everyday people experience this state. I took another look after listening to the interview on Buddhist Geeks, Mapping The Mindful Brain.
This would appear to be feedback based on decreased activation of the posterior cingulate cortex (PCC), which would be roughly the area of Pz on a 10-20 brain map. I'm not sure that EEG feedback can reach this quite in the same way the fMRI can, and I've seen mixed results for studies correlating fMRI with EEG amplitudes in that area, some saying alpha is positively correlated, others negative. Not sure there is a clear path there yet.
It does seem logically, that we want to quiet the brain in that area, and alpha-theta training at Pz would seem to be something along those lines.