I think (and don't quote me on this), you can't actually mount the shocks to the rear without great modification.
This has been tried by a number of people but it involves swapping the wishbones over and shaving quite a bit off of the rear edge to move the arms rearward enough so that the shocks will mount without any strange angles involved. You also need longer screws and some more washers to mount the shocks.
It sweeps the arms forward shortening the wheelbase and, like you say, mounts the shocks to the rear of the shock tower.
I found that it makes the car twichy and not as good over the bumps (although others prefered it) but when you get the set up good, it makes it really quick through the corners.
But I can't see of a way to mount them behind the rear arms without modding the gear box tops etc. or using the method above, because you'd have to move the shock mount.
