Flexible engines with stub partials

Hi,

I am designing a e-commerce engine which must be very flexible. I am
keeping each template and partial small for easy overriding but in
some cases I’d like to do less work to extend the engine. I’m thinking
about using some stub partials. This would be a blank .rhtml file in
the engine and rendered in one of the templates. This would be a nice
hook for the engine user. One useful example I can imagine is having
a hook in the layout head so extra js and css files can be used
without rewriting the layout.

Has anyone done this before? Any other approches or advice?

Thanks,
Peter