> Sounds like something I would *not* do. If you are going to return a
> 404, why not do it as soon as possible.
> Generating data only to return a 404 sounds like useless extra work
> unless you are caching the same data for future requests.

I agree, if you don't want to much up your data generation code, write
an Access or Fixup Handler (or any other pre-response phase handler of
your choice) checks for the existence of the template at that stage. If
it's not there, 404.