In the main method, then you can pass the configured values wherever you need to when new-ing classes.

> At some point you want a user-facing UI where the available features (which are generally classes) are listed and the user can choose the feature, say which log backend is enabled, without having to change code - that's the whole point of it. (And the most tedious code to write by hand - a complete waste of time)

I consider DI a valuable pattern, but I've never experienced anything close to this need.