Why do you need mod_perl?
Most server configurations have no need for mod_perl because you
do not need it in order to run and fully support Perl scripts.
In the same vain, there are better ways to run PHP than as a plain
insecure Apache module. I personally would recommend SuPHP
for those on Apache 2 but if you aren't on Apache 2 then you might
want to consider phpSuExec.
Bottom line though it is extremely rare for you to actually legitimately
need both mod_perl and mod_php so I am a bit curious as to what
you are specifically wanting to do on the server that needs those.