A better way to break up an interface to divide concerns

A better way to break up an interface to divide concerns

I'm attempting to normalize the WCF Data Services object model to make it
more approachable for my team and would like to breakout the
System.Data.Services.IUpdatable interface into more concern-specific
pieces. To eliminate my personal constraints and situation from this
question, I've prepared a similar yet unrelated example to help depict the
problem.
Imagine you are asked to implement a 3rd party repository interface
similar to the following:
public interface IDataSource
{
#region Item-centric Methods
object GetValue(object target, string property);
void SetValue(object target, string property, object value);