how to permit the "?" and "=" in the url ?

[eluser]quasiperfect[/eluser]
tried

Code:

$config['permitted_uri_chars'] = 'a-z 0-9~%.:_\-\?=';

i get a 404
my url is like this

Code:

http://localhost/codeigniter/controler/method/?var=value

i don't need anything after the method

i only need this for 3 controllers and idea i would love not to enable qs and permit the chars globally but i have no choice i need this for some flash files that are compiled and i have no source