I asked Byron http://byron76.blogspot.co.uk/ and he suggested looking into PSKeys, and I believe that it is not possible with the current firmware (or the ones out there) to set the HC-05 to non-discoverable mode. It does seem that Bluesuite's PSTool (or command line) is required and perhaps some USB -> SPI with some soldering to turn this mode on.
If anyone knows that this has already been implemented in a firmware update or there's a undocumented AT command then I'm happy otherwise the above is the route.