Another cable compression solution.

[stevewaters]

This is the side view. I had 2 x Nukeproof 25mm spacers beneath the Love Mud stem and I swapped the lower of these spacers for the Accessory Bar. The Accessory Bar itself seems a well made and solid item - no worries about tightening up the harness straps or limiting the luggage weight.
I put an old blue lock-on MTB grip end on each end of the Accessory Bar to prevent the harness straps from sliding off.

[belugabob]

Thanks - that's clinched it, for me.