I thought I would post this separately to make it easier to find because the other post is a review of the Capture Pro clip.
When I first picked up my Blackrapid shoulder strap, I had issues trying to get an arca swiss setup going. I wanted to leave my arca swiss plate on so I wouldn't have to remove it every time I wanted to use the strap. In the end, I had to buy a arca swiss clamp which was not cheap and adds extra weight if it's a decent model.
When reviewing the Capture Pro clip, I noticed it comes with the new Pro Plate (which they sell separately) and the pro plate includes a load bearing ring which folds flat. It's both arca and RC2 compativle. This means you can simply buy the plate (instead of another brand of plate which will cost the same anyway), and connect it to your blackrapid strap.
Only downside is that you can use your own L plate.
While looking at this, I also noticed there is an alternative which also started as a kickstarter project. It's a bit more expensive but looks like a better option for things like 70-200 mount plates. You can see it here
Here is the plate with the ring attachment. I'd still recommend the use of a leash. Peak offer a sling with a nice quick release systems but I use a carabiner setup I bought from a climbing shop. I guess you just need to be confident the leash will hold.