aserve condition handling question

I have a bunch of pages that display results of database queries whose
parameters come from GET requests. Since the links pointing to these
pages are generated from the same database, generally there should be
no problems with the input parameters. But just in case someone
bookmarks these pages, I'd like to handle 'bad' parameters, too, and
do this uniformly for all these pages.

I don't know if this is relevant, but these pages are published with
publish-multi, and ideally, only one item should be affected (i.e.,
there are a standard header and footer as separate items, which should
display no matter what, but instead of the dynamic part, I'd want to
show an error message).

Is this possible without using, say, handler-case on each page? I
could ease that with a with-good-input-only macro, but I wonder if
there's a way to set up a handler in some central place. My very
limited understanding of the condition system tells me that this would
only be possible by changing the way aserve calls the functions that
provide items in a publish-multi.

Andras