Dynamic metal includes?

Hi

I have tried out the include stuff recently talked about on this list, but I don't think it does exactly what I want.

What I'm looking for is something like

<!-- fancy html --> 
  <div tal:replace="insert: $page">__MAIN__</div>
<!-- fancy html -->

where page is a macro like #index_body for example

At the minute, what I'm doing is 
<!-- fancy html -->
 <div tal:if="eq: $page string:help">
  <div metal:use-macro="#help">__MAIN__</div>
 </div>
<!-- fancy html -->

Thanks for any pointers

Simon