You can hear it on the wayback machine (Internet Archive). It's included in the "John Lennon - Home Demos 1975-1980 (Vol 1)" and also includes the bridge McCartney cut.So, a question...
Why was it so important to separate Lennon's vocals from the piano?
Would the song have worked simply by taking his original recording of him singing at the piano and adding the rest of the modern instrumentals and voices?
The only thing I can think of is that the song would not have worked as well with the piano constantly being present in the recording.