Been playing this one since this version came out. The end is simply a modulation up. Just figure the last chord of the quad involved, play the last one as a passing chord and start on the new "one". If you were in "C", the passing chord would be A flat, followed by the "one", which would be a "C#".
It would be a 1/2 step modulation.
This is a good example of interpretation and, of course, talent.
Good find!
Russ