All args must be specified in the route, but can be made optional. In this instance you may want to change the default route to something like...
Route::set('default', '(<controller>(/<action>(/<arg1>(/<arg2>(/<arg3>(/<arg4>))))))');
You can then reference the args by using "request"...
$this->request->param('arg1');
$this->request->param('arg2');
$this->request->param('arg3');
$this->request->param('arg4');
You could obviously have more than 4 if you needed them.