I found that he often mixed two approaches to make his chord solo melodies,
especially on the iim7 chords (Wes would often use the minor chord idea over
both the iim7 and V7th chord and not switch to dominant chords on the V7
measure while chord soloing).
As an example of a iim7 chord in G major (in Round Midnight these ideas were
in Gb major):
#1.) on the Am7 chord Wes would play alternating inversions of Am7(ACEG), and
Bm7(BDF#A), (the iim7 and iiim7 chords in G major). If laid in a scale order
these chords' melody notes would spell out the scale A,B,C,D,E,F#,G,A (the A
Dorian scale). This method is something I hear piano players play all the
time in modal situations like "So What" or "Impressions."
#2) Wes would also use the Aminor 7th chord and all its inversions combined
with a B diminished chord (a whole step above the root of the minor 7th
chord) through all its inversions:
on Am7 the resultant combined scale for the melody notes would be
A,B,C,D,E,F,G, Ab (a scale containing eight notes).
Wes also used some common devices like sliding into chords from a half step
above or below (the target chord usually on the beat and the approach chord
on the "and" of the previous beat).
I have found that if I practice these two simple chord scales until they are
fluid it is pretty easy to use them to create melodies in the same way that
single note scales are used to create melodies. I don't have to use
pre-memorized chord licks, I can create melodies in a more "in the moment"
way.
Brian Oates