routing with encoded forward slash

[eluser]enition[/eluser]
Do you know of a cleaner way to do the same as this?

$route['part/([a-zA-Z0-9]+)'] = "product/lookup/$1";
$route['part/([a-zA-Z0-9]+)/([a-zA-Z0-9]+)'] = "product/lookup/$1--$2";
$route['part/([a-zA-Z0-9]+)/([a-zA-Z0-9]+)/([a-zA-Z0-9]+)'] = "product/lookup/$1--$2--$3";
$route['part/([a-zA-Z0-9]+)/([a-zA-Z0-9]+)/([a-zA-Z0-9]+)/([a-zA-Z0-9]+)'] = "product/lookup/$1--$2--$3--$4";

like i said.. rubbish at regular expressions!