The DocumentManager class is intended to be constructed through its create()
static factory method, as is shown in the Getting Started and Introduction documentation entries.
Taking a look at Flight's Registering Classes, it only appears to support constructing classes by invoking their constructor. This is in contrast to frameworks such as Silex, which allow you full control over constructing your shared services (see here). As-is, I don't see a work-around within Flight's current code, so I would suggest opening an issue or submitting a pull request to the project to request/add more flexible service construction.