The first step in shoe-mount flash light output modification is to remove the flash from the camera's hot-shoe. By mounting the flash on a light stand or camera bracket, the light is less directional and blunt as the flash's output path no longer closely match the camera's optical path.
To facilitate this move, a cable like this Dot-Line RPS Swivel Mount TTL Cord for Canon eTTL acts like an extension cord and provides up to 2 meter of distance between the camera and the flash without any stipulations.
Functionally speaking, this cable features a swiveling mount that lets a flash head pivot, even when it inherently lacks that ability to do so on its own. Furthermore, the cord is mountable on a light stand as easily as it nests in an accessory shoe. A 1/4"-20 female thread provides yet another mounting option.