Upload & Sell: On
The best solution that I have found is a combination of a modified Black Rapid strap connected to one long lens, and the other long lens with a regular lens strap slung over the opposite shoulder. I carry a 600/4 on the BR and a 300/2.8 on the strap.
I modified the BR by adding a second fastener and connector. The first connector is screwed into a small clamp that clamps onto the lens plate, and the second connector is screwed into the bottom of the camera. By adjusting the distance between the two connectors (done by sliding the clamp along the lens plate), I can make the lens hang vertically at my side or kind of horizontally.
The second lens and camera are slung over the opposite shoulder. I'm using a CPS strap because I find it very well padded and it has a good length that allows me to bring the camera to my eye without the BR getting in the way, but it isn't so long that the camera and lens swing at my side.
Kind of hard to describe in words, but I hope you get the picture.
EDIT: Andy's point about the double BR is good, but I found that both rigs tend to swing too much. Didn't work for me, but YMMV.