I don't know if encode_entities_numeric() can do it, but if it can't, here is a way to post-process the results:

use warnings;
use strict;

my $str = "some special chars like € ™ © ®";
$str =~ s/&#x([[:xdigit:]]+)/'&#' . hex($1)/eg;
print "$str\n";

__END__

some special chars like € ™ © ®
[download]