A separate server process which the mod_perl Apache processes talk to is probably the "ultimate" answer. When some nice person names the perfect CPAN module to implement that kind of server, I'll certainly bookmark it myself (and give you a grateful thought).

Otherwise, I have used the PerlModule command in a <IfModule mod_perl.c> stanza in httpd.conf.

I didn't need to do more. The Perl module is read in at Apache start and the memory is shared with sub Apache processes.