Watch the Keep Cool online guitar lesson by Brad Carlton from Chord Studies: Jazz Turnarounds Vol. 3
Our first chord here is a four-voice Fmaj7. Note the soprano tone here (C) as it's going to remain as our top tone throughout. We go to the vi chord applying the b5 substitution principle, and then go to the ii chord but because of the C voice it becomes a Gm7/11. All I have to do is move the third and fourth voices down and that gives me the b5 sub of my C7.