I'm a little confused on what is being asked...If it's the key of Eb, it seems its been assumed the bass is C, making the first chord Cm9, but no bass note was given in the original post...So lets just say it's an EbM7, the progression being 1-5-4...
Couldn't you do both 1-2-5-1-4 or also 1-2-5-b5-4...to me it would be a question of how much you would want to throw in the progression, how much time is allowed...ie, placement and chord selection.