Watch the Try Tone online guitar lesson by Chris Buono from Guitar Lab: Blues Progressions
Back in The Wes Coast you came across a harmonic movement in bar 4 that may have thrown you for a loop at first sight. But, after playing it I'm confident the hip sound you heard as a result of such a move put a smile on your face. The sound I'm alluding to falls under the concept of tritone substitution. Put simply tritone subs are chords whose root notes are replaced by a note a #4/b5 away. The space in steps between the root and #4/b5 is three whole steps hence the name "tritone".
Throughout Blues Progressions the concept of voice leading is treated with reverence and that surely won't stop here in Try Tone. In fact, it's what makes the idea of tritone subs work that much more. Be sure to closely examine the chords and how they fit together so when you design your own progressions or simply drop tritone subs on the spot they sound as cool as they should.