This currently requires modifying the source code, building it yourself, and using binaries currently only available in private testing. I think that maidsafe intend to make this easier for developers who need it though, so keep an eye on the developer updates (every Thursday by about 20:00 GMT, unless David keeps @Krishna_Kumar & @Shankar up through the night like last week, when 11pm for us meant 4am for them!)
I made a safe_vault fork allowing local networks. See instructions here.
To get the client binaries to access the network you need to reach the trust level 2 in this forum.
