Just a thought, but how about you remove the lock, and relocate the contents “somewhere else that is secure”, and leave a note advising that the contents were left on your property, your contact details, and the length of time that you will keep them for (I think the standard required is 3 months).
I would expect that the owner would start to care when their property vanished 😉
One problem is that things in “storage” may rarely (if ever) get touched, and depending on the location of the storage cage, the owner of the contents may not see any notice, assuming they still live in the building/etc.