derived models are meant for hierarchical projections on entity models. You can't map an entity onto stored procedure resultsets, only typed views, which don't have relationships so it's kind of moot: it would be just another typed view mapped on the typed view.
If you're looking at mapping a poco class on a stored proc resultset, you can, just map a typedview on it and set its 'Output type' in code generation info to 'PocoWithQuerySpecQuery'.
In v5.1 an easier way to do custom projections will be introduced, including a way to call a stored procedure in a micro-orm way using raw SQL. This will help with doing projections of stored procedure resultsets to custom classes without needing a lot of code.
