This is one that got dropped down on me over the weekend, causing my runs to sky-rocket. It's nothing that new, but I'm just now understanding how sweet it is.
Ok. Here is the secret: use the major scale that begins a whole step below the key you're in. Check out the example using the key of F.
Key: F
F / Eb-G-Bb-D-F
RUN: Ab, Bb, C, D, Eb, F, G, Ab - "Ab Lydian"
A / G-B-Db-F
RUN: A, Bb, C, D, Eb, F, G, Ab, Bb, C - "Bb Mixolydian" with an extension to C
Bb / Ab-C-D-F
RUN: C, D, Eb, F, G, Ab, Bb, C, D, Eb, F, Eb, D, C, Bb, Ab - "C Aeolian" with a decending F Dorian
You can also switch to the keys of Bb or Eb and use chords from each.
B / Ab-B-D-F
RUN (Decending): Bb, Ab, G, F, Eb, D, C, Bb, Ab - "Bb Mixolydian" extension to Ab
F-G / Ab-C-E-G
You can change the "E" to "Eb" if you want.
You can even run the two scales on top of each other. Try playing the Eb scale starting from Ab, while you play a normal F scale in the bass. Sweet!
I do some things extra, like running the scale up and down or throwing in chromatics, every now and then, but it all works around that Eb scale. To do the runs fast, your thumb has always land on C or F. If it touches any of the other keys, your speed will be limited.
I'll post a clip later. I have a working video camera now.