Routing: Passing entire expression as unique argument

[eluser]Unknown[/eluser]
Hello, I'm trying various configurations with the Code Igniter routing feature. I'm developing a filebrowser-like webapp, and my goal is:

Given this URL:
http://example.com/app/controller/method/path/to/file

I want that CodeIgniter call my method on controller passing it the rest of the url (something like $controller->method("path/to/file")

I tried with:
$route['controller/method/(:any)'] = "controller/method/$1";

and
$route['controller/method/(.*)$'] = "controller/method/$1";

But I only get the first path component as argument to my method. (I tried various regexes and nothing)

How can I get this behaviour?

Thank you