Tom found an alternative to the Signum cable manager. His uses the Antonius clothes hanger. If you don't have a lot of cables, this could be ideal.
"I recently found a nifty solution for the crippling problem of cable management. It might not be suitable for super computers but it does work for my desk. It was built by screwing Ikea Antonius coat hangers to the underside of the desk using long enough wood screws. To give it a bit of stability, I used a hollow tube (like piping cut to length) for the hangers to sit on."