I'm building an application in the Zend Framework, but I'd like to implement a "Data Mapper" style ORM layer, constructing Model classes that only include the specific pieces of data they need to represent the domain concept (regardless of which tables those fields happen to belong to). Since my DB structure is highly normalized, the benefits gained from an Active Record ORM would be superficial.
So how would you implement a very simple, straightforward data mapper ORM layer in the Zend Framework?