[web2py] Conditional {{extend layout.html}}?

[Simon Ashley]

Wondering if it is possible to have a conditional {{extend layout.html}} 
similar to the following?

 {{if session.call:}}
  {{extend 'layout_XXX.html'}}
  {{pass}}

{{if not session.call:}}
  {{extend 'layout.html'}}
  {{include 'YYY.html'}}
  {{pass}}

....

Required for users with requiring different configurations. 
Have tried alternative approaches without success.
TIA

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