Overriding an abstract property with a derived return type in c#

I have four classes. Request, DerivedRequest, Handler, DerivedHandler. The Handler class has a property with the following declaration:

public abstract Request request { get; set; }

The DerivedHandler needs to override this property so that it returns DerivedRequest instead:

public override DerivedRequest request { get; set; }

Does anyone have any ideas about how to make this work?