Adding a Configuration at runtime

Question

I'd like to add a configuration within a plugin at runtime and probably also register it at projectConfigurations. Is there a possibility to manipulate the state in such a way? I assume this needs to be done in a command, and the solution is buried somewhere deep inside of the AttributeMap, but I'm not sure how to approach that beast.

def addConfiguration = Command.single( "add-configuration" )( ( state, configuration ) => {
    val extracted = Project extract state
    val c = configurations.apply( configuration )
    // Add c to the state ...
    ???
} )

Background

I'm working on a sbt-slick-codegen plugin, which has multi-database support as an essential feature. Now to configure databases in sbt, I took a very simple approach: everything is stuffed into a Map.

databases in SlickCodegen ++= Map(
    "default" -> Database(
        Authentication(
            url = "jdbc:postgresql://localhost:5432/db",
            username = Some( "db_user_123" ),
            password = Some( "p@assw0rd" )
        ),
        Driver(
            jdbc = "org.postgresql.Driver",
            slick = slick.driver.PostgresDriver,
            user = Some( "com.example.MySlickProfile" )
        ),
        container = "Tables",
        generator = new SourceCodeGenerator( _ ),
        identifier = Some( "com.example" ),
        excludes = Seq( "play_evolutions" ),
        cache = true
    ),
     "user_db" -> Database( ... )
)

Now, this works, but defeats the purpose of sbt, is hard to setup, difficult to maintain and update. I'd instead prefer configuration to work like this:

container in Database := "MyDefaultName",
url in Database( "backup" ) := "jdbc:postgresql://localhost:5432/database",
cache in Database( "default" ) := false

And also this approach is working on the current development branch, but only for Database( x )-configurations that are known at compile time, which leads to the next problem:

On top of that, I'm planning to add a module with PlayFramework support. The idea is to have a setting SettingKey[Seq[Config]]( "configurations" ) that accepts Typesafe Config instances, reads the slick configurations from them and generates appropriate Database( x )-configurations. But for this step I am out of ideas.