Think of your G7b9 as being an Ab diminished chord with a G bass. If you would shift the bass note only to Bb then you would have Abdim/Bb aka a Bb7b9 - which would be the dominant for Eb major. The chords are so related as to be interchangeable.

It's a standard jazz piano practice to shift dominant 7th b9 chords by m3rds - to get motion in the comping - regardless of the root the bass player is holding (Herbie Hancock). Your progression strikes me as very similar.

Of course the standard way to modulate up from C to Eb would be- Cmaj7 Fm7 Bb7 Ebmaj7. Circle of fifths. Take the Fm7 Bb7 and do a tritone sub - becomes Cmaj7 B-7 E7 Ebmaj7. Similarly subs on the m3rds are not so uncommon - but not unheard of either.

Cheers