We got a few local Model S owners together and we created a Roadster HPC to Model S adapter share group. We pooled some money for an adapter, a locking NEMA box and the contributing members have the combination to the box.
We got permission from the property owner to mount the box at their facility and sought out the owner of the HPC for permission. No one admitted to being the owner and the person who owned the property thought that the charger was provided by Tesla. (I'm pretty sure that it was a generous Roadster owner though.) The property owner did the original HPC install to draw customers to their restaurant and volunteered to mount the adapter box too. Once Superchargers were put in service close to the Roadster HPC we moved the adapter to another HPC location that was in need of an adapter.
You might consider doing the same. A few of the adapter share people ended up getting their own adapters once they realized what they were missing.