use corrugated split loom, or even the wire braid(this is harder to pull over bundles of wire, then split loom) and then try these clips, these are what normally come stock, and don't require you to remove completely to fix/add to the loom.
http://www.clipsandfasteners.com/Clips_Wire_Loom_s/78.htmsplit loom is also easier to branch off, just pull the wire out, and throw a little electrical tape around loom on either side of the wire to prevent it from coming all the way out