I have figured out how to do it. Well I didn't figure it out I kind of found it. Anyway, here is the solution.

# --- Stolen shamelessly from XML::SAX
package MY; # so that "SUPER" works right
sub MY::install
{
    package MY;
    my $script = shift->SUPER::install(@_);
    $script =~ s/install :: (.*)$/install :: $1 install_libmyfoo/m;
    $script .= <<"INSTALL";

install_libmyfoo :
\t\@mkdir -p \$(PREFIX)\/lib && cp libmyfoo.so \$(PREFIX)\/lib

INSTALL

    return $script;
}
[download]

That goes below the "WriteMakefile" function. It modifies the install target (it actually adds a install_libmyfoo target) to move the .so into its proper position.

Cheers!
--habit