Note: new releases are up that include WatchedEntity:
You grab a WatchedEntity in a similar way to an entity set except that you give it a specific entity ID.
WatchedEntity ship = ed.watchEntity(shipId, Position.class, Model.class);
You can then use it exactly like any other Entity, calling set/get on it. In this case, if the entity doesn't have a component then get() will return null.
Where it differs from a regular entity is that you can call applyChanges() on it to get the latest component values.
It's precisely designed to cover cases like the player avatar, player status, player ship, etc... the thing you will know you have exactly one of and need to deal with that one thing directly and using an EntitySet of one item is clumsy.