With "can't change my setup" I meant I can't update my Apache/mod_perl/OS (at least unless someone tells me that this is a bug that has been fixed in some later version, so I can apply pressure on the server/perl packaging folks...)

If this is an apache/mod_perl bug (which seems likely, given how old your apache is), it seems so esoteric that I'd despair of finding a reference to it in the changelog. Have you tried a newer version of apache yourself? You can build one in a nonstandard location without needing root access. Surely you must have a suitable development machine somewhere you can try this out on.