set config item 'permitted_uri_chars' individually for a specific controller ?

[eluser]mmackay[/eluser]
Hi there, I'm keen on keeping the default permitted characters globally for my CI install but on one controller I really need to allow flexibility on what characters are permitted for the URI.

Is there any way to set the item dynamically when required in the necessary controller(s) ? I tried using $this->config->set_item('permitted_uri_chars', 'xxxx'); but it had no effect.

Is it at all possible ?

Thanks.

- Mike