I dive a DIR configuration with an Ikelite housing and dual Ikelite strobes. On each of my Ikelite tray extender arms, just below the ball joint, I used nylon rope and made a small loop. Each of these loops provide me a place to clip a double ender. Typically, I clip off my camera rig to my left shoulder d-ring using one of the nylon rope loops. Due to the camera rig being negatively buoyant, the camera rig will just dangle from the d-ring. I have no problem swimming in this position and this is how I clip off my camera most of the time.
However, if I am swimming just above a reef or sand (i.e. the camera rig might drag in the sand or on the reef), if there is a possible entanglement hazard (i.e. lots of kelp) or if I have a challenging surf entry or exit, I will clip the other end of my camera rig to my waist d-ring. This way, the rig is secured by two points to my harness, is now parallel with my body and unable to freely move about.
If I am diving my Sierra scooter, I would not bring this camera rig. I have not figured out any way that I could effectively scooter while operating a camera rig that requires two hands. Instead, I mount a small point and shoot camera on my scooter.
