I asked you the variants as you will not want to do .net if you had not before ! why bother with Plex.Net Server ???
What is your architecture?
CA Plex Help "Connecting to Multiple Databases"
"The database connection used by a given function can be specified at design-time (by means of DB connection name triples) or it can be switched dynamically at run-time using a SetDatabaseConnectionName API. Database connections are stored as logical names whose details are kept in the application's config file (for C# applications), .properties file (for Java applications), INI file (for Windows C++ clients) or the registry (for Windows C++ servers)."
I use extensively 'SetDatabaseConnectionName' the manual method in AutoTestBox - Stella Tools (CA Plex Developer Tools)
OR
design time using DB connection name triples which unlike Lorenz I guess you are using either of these two INI file (for Windows C++ clients) or the registry (for Windows C++ servers)."