Okay, what i am trying to achieve is simply not there.
BuildOption._docs is a enum, that is passed recursively to the dependencies and switches doc building on and object building off for the different generators (I missed to say that i am using dmd -> "-o-", "-Dddocs").
What i was looking for is a dub command-target like "build", "run", "test".
Oh .... "add docs command" -> https://github.com/dlang/dub/issues/501
Not a solution, but a warm feeling of knowledge:)
