The bracket which came with my lock was (as with most I've ever seen) rubbish, insecure & would have prevented me mounting any water bottle cages. However I don't like always having to have a bag with me when I cycle or putting a wet lock (if my bikes been locked up out in the rain) in my bag so I came up with this.
• PVC Conduit - As close a fit as possible to the U part of the lock. I got a suitable 2m length for £1.70 from B&Q
• Hose clamps - 4x 10mm and 2 or possibly 4 x 22mm (sizes will vary according to your rack & lock diameters)*
• Bits of old inner tube or other material to make shims
• Zip ties - 2
*The hose clamps need to be reasonably robust I initially used some from Aldi which were soft and thin and not up to the job. I got some more substantial ones from Screwfix which seem just fine.
Step 1: Cut conduit to length
The conduit should be of a length where it's outer edge is pretty much flush with the lock mechanism. If the conduit is too long you obviously won't be able to attach the lock, too short and the lock could move about when you ride.
Step 2: Bevel the inside edge of the conduit.
This makes it easier to insert the shackle into the bracket and is easily done with a stanley knife.
Step 3: Prepare attachment points on rack
I'd have preferred to use hose clamps to hold the conduit at the rear fixture as well but the strut on the rack was at too much of an angle to I used zip ties instead.
Step 4: Attach the pieces of conduit.
Slide the conduit pieces onto the shackle then slide the shackle into the attachment points on the rack. Find a position for the lock where it doesn't interfere with your panniers. Tighten everything up.