I've adopted the 'rope access' method of cowstails with a very short loop between the two normal lengths - this has a snapgate on, specifically for downward rebelays. I use screwgates on the main two, in case I have to 'hang around' and for extra security generally. It's virtually impossible for the snapgate to come off, as it's always loaded. The main advantage is that the distance you need to stand up to unload it is negligible, and makes multiple downward rebelays a lot less tiring.
I use a maillon to connect my jammer to the harness, and if I need to use the jammer to stand up with at rebelays, I put a steel krab into the maillon, and then clip the krab into the bolt. I don't like the idea of having the jammer permanently on the krab only, as the possibility of dropping the jammer is much higher!