SetEnv PERL5LIB /where/the/mods/are/:/where/else/lib

##</code><code>##

#!/usr/bin/perl -w
use CGI ':standard';

# Newly inserted
BEGIN {
    if ( $ENV{PERL5LIB} and $ENV{PERL5LIB} =~ /^(.*)$/ ) {

        # Blindly untaint.  Taintchecking is to protect
        # from Web data; 
        # the environment is under our control.
        eval "use lib '$_';" foreach ( 
            reverse
            split( /:/, $1 )          
        );
    }
}

use Mail::Sendmail;

# The rest of the script....