How to imitate yield functionality like WWW class

Hi guys,

I'd like to write a class that can act the same as WWW in its ability to pop back into processing once it has done it's deed by yielding the instance itself.

So I want to do the exact same as:

 WWW w = new WWW("no matter");
 yield return w; // Wait for instance

(I wish to use my own class instead of WWW)

And not:

 Tesy1 t = new Test1("no matter");
 yield return StartCoroutine(t.someMethod); // wait for method in instance

How would I go about doing that?

Thanks.