Dependency Injection With OpenWhisk PHP

Any non-trivial PHP applications use various components to do their work, from PDO through to classes from Packagist. It’s fairly common in a standard PHP application to use Dependency Injection to configure and load these classes when necessary. How do we do this in a serverless environment such as OpenWhisk?
This question comes up because we do not have a single entry point into our application, instead, we have one entry point per action. If we’re using Serverless to write an API, then we probably have a set of actions for reading, creating, updating and deleting resources all within the same project.