Originally Posted by MichaelW

Secure a bunjee chord across the top of the rack.
Put the lock under the bungee chord.
Jamb the curved end of the shackle under the raised front loop of your rack.
If you rack has a solid top plate and no open loop (as in Medic Zero's rack) then change it for one that does.
This fitting is totally secure with no rattling, provides instant access to the lock for locking or anything else and does not interfere with bags. You do have to lock before removing bags and attach bags before stowing lock, but this is the natural order of things.