Easiest way to expose existing data in secondary database as entities? Given a "node-like" database table in an "external" or "secondary" database, what's the easiest way to expose them as entities?

Documentation for the entity module makes it seem easy for data stored in the local database, but I'm not sure how that can be translated to another db.
Some googling has revealed that the easiest solution is


Declare a new entity
Create a new Controller class for it that knows how/where to apply data operations.
Declare all your metadata as properties as opposed to fields.


I hope I'll be able to expand on this answer once I actually try it out. :)