Another option might be to write a (somewhat) simple web service as a front end to the database.  A BOS can communicate with any number of web services, and you'd avoid the security issues of directly exposing the database.  This is actually an option several other customers use.   For read-only access this might entail very little coding, since you could also use DevForce to generate the web service.   For update access it's a little more difficult, but still doable.   We have several web service instructional units available - on "publishing" and "consuming" - and a sample available by request showing how entity updates can be accomplished.

 

You can, however, set the PersistenceServiceOption argument when you create a PersistenceManager.  This defaults to using whatever is specified in the config, but you can override it to specify that the particular PM use only local or only remote data sources.  This is primarily useful when you will usually be using a BOS but also need to use a local database.

 

In your case, if you can always access the main database from the client with a direct 2-tier connection to the database, then maybe the PersistenceServiceOption will work for you.  You can contact us directly if you'd like to discuss your options further.