Hi Bruno,
You can use the client package from the server with embedded policy. What this does is contact the server one time upon enrollment and then the client will never contact the server.
The next step would be to change the PGP stamp to PGP Default Stamp. This will make your client stand-alone with the policy that you set on the server when you downloaded the client package with preset policy.
Some companies do this if there client never checks in with the domain or the office. Usually they'll put the WDE Admin enabled on the policy so if the user is locked out of their computer then they would have to bring there computer back to the company for the Admin to unlock.
If you just want a complete stand alone with no embedded policy then download the file from file connect. The file is called SymantecEncryptionDesktop10.3.1_MacOSX.tar.gz
Thanks
Anthony