In reply to two_tapirs:
I believe the Petzl Calidris was meant to be good for this, with it's odd double waist-belt design at the back to spread the load. It's been around a long time, but looking at the Petzl website I see they still make them.
Assuming I can find it, I have a rather old but little-used one kicking about somewhere that you'd be welcome to try*. Or indeed keep if it works well. I never got on with the gear loops, and eventually replaced it with a WC Syncro while it was still relatively new.
I'm in Sheff, frequently work in Manchester/Leeds and round about. Could drop off at a wall somewhere perhaps?
* - Obviously the usual caveats about second-hand gear apply. Someone will be along shortly, quite possibly, to tell you that you're going to DIE if you so much as try it on. I'd be happy enough to use it again though - I'm pretty sure it's been sitting in the garage in a plastic box for some years. (Next to the big pile of old car batteries, just under the leaky bleach-bottle shelf. ;O)