Forwarding or merging 'this' into a child class to aid chaining methods?

[Gary Willoughby]

I'm trying to create methods across class hierarchies that can be 
chained nicely but i'm running into the problem that 'this' 
declared in a parent class only refers to that type. Is there a 
way i can get the following code to perform in the way i expect?

import std.stdio;
class Foo
{
        public auto foo()
        {
                return this;
        }
}

class Bar : Foo
{
        public auto bar()
        {
                return this;
        }
}

void main(string[] args)
{
        Bar bar = new Bar().bar().foo();
}

test2.d(21): Error: cannot implicitly convert expression ((new 
Bar).bar().foo()) of type test2.Foo to test2.Bar
Failed: 'dmd' '-v' '-o-' 'test2.d' '-I.'

How can i make the above marked 'this' refer to Bar when being 
called in a chain? When i call the methods like this each method 
call seems to implicitly convert 'this' into that method's 
containing class' instance, breaking the code and sometimes 
hiding child methods.