Unless you are only rarely using these particular modules, you aren't going to see any gain from this. Maybe you can fork a child, have it import and do the large module import and then pipe it back to the perl process.

Or (insert random deity here)-forbid you just use a CGI for the module-intensive, only-run-occasionally code. What you want to do with memory just can't be done. I've seen this same struggle over the past three years with mod_perl (admittedly you've gone a lot further than most... =) but in the end, neither perl nor the most common OSes make it easy to return memory.

Ideally, use mod_perl on code that needs the extra speed of already being available in the server, code that needs access to the request at early stages, and code that needs special persistence. If the code isn't basically continually being run, you are likely to be wasting your time mod_perl'ing it.

--
$you = new YOU;
honk() if $you->love(perl)