use Module::ScanDeps;

my $perl_script = 'whatever.pl';

my $hash_ref = scan_deps($perl_script);

for (keys %$hash_ref){
    print $_,"\n" if ( $$hash_ref{$_}{'file'} =~ m#/site/# and $_ =~ m#\.pm# );
}

# Only capture the name if it IS a module (.pm) and it 
# isn't in core, (path includes /site/). You may need 
# to modify the filter if your modules are in non-standard
# places.