unlikely...

I use a key:value pair in my URI to distinguish required variables.
It looks like this: http://www.yourwebsite.com/controller/me...ar_id:1234

For this I have extended the core URI class and have a method that searches for key:value pairs in each available uri segment.
If a segment is a key:value pair, it is removed from the segments array, and I rebuild the URI segments array.

The found pairs are stored in an array params.
So your webinar_id would be stored as:

PHP Code:

$this->params['webinar_id'] = 1234; 


Below are the methods that I use.

Find the key:value pairs

PHP Code:

/**
 * Method to extract key:value params from the url
 */
private function _set_params() {
    if(count($this->segments) > 0) {
        foreach($this->segments as $key => $segment) {
            if( strpos($segment, ':') ) {
                list($key_name, $value) = explode(':', $segment);
                if(is_numeric($value)) {
                    $this->params[$key_name] = (int)$value;
                } else {
                    $this->params[$key_name] = $value;
                }
                $this->_unset($key);
            }
        }
    }
} 


Reset the URI segment array

PHP Code:

/**
* Method to reindex the segments array after any unset()
*/
private function _unset($key) {
   // Check if the key exists in the segments array
   if( array_key_exists($key, $this->segments) ) {
       // Unset the passed key
       unset($this->segments[$key]);

       // re-index the segments array
       $nkey = 1;
       $segments = $this->segments;
       $this->segments = array();
       foreach($segments as $segment) {
           $this->segments[$nkey] = $segment;
           $nkey++;
       }
    }
} 


Get all available parameters

PHP Code:

/**
* Return the set parameters
*/
public function get_params() {
   return $this->params;
} 


Get a specific parameter

PHP Code:

/**
 * Return a set param
 */
public function get_param($key) {
    if( array_key_exists($key, $this->params) ) {
        return $this->params[$key];
    }
    return NULL;
} 


To get the value of webinar_id in your controllers method, or any method in any class just do:

PHP Code:

$webinar_id = $this->uri->get_param('webinar_id'); 


All of the above methods are placed in the extended core URI class MY_URI

Hope this can help you out