I don't have a cage so at present my harnesses are secured to the chassis/floor with the traditional eye-bolts. At the end of each harness strap is a buckle and then a hook (cant think of a better word for it) fixing. The strap threads through a slot in the hook fixing and then back into the buckle. What I am suggesting is that you simply unwrap the strap from the buckle, remove the hook fixing, wrap the strap around the cage and then back into the buckle. There are not cage and eye-bolt hook specific harnesses, they are all the same, if you don't need the hook you simply remove it.