Looking for a way to avoid DoubleRenderError

The “update” action of my controllers and under certain circumstances
creates a xml file on the filesystem.

Using an after_filter that only gets called after the update action I
create the XML file.

Problem is, I get a DoubleRenderError because the update action either
calls redirect_to or render. I can get around the render call by calling
performed?() but the call to redirect_to always chokes the rendering of
the xml file.

Any ideas on how I can achieve this behaviour ? Or is there a more
railish way to do the same thing ?