How do I set up a route that sometimes has a parameter and sometimes
doesn't? For example, I have the following two routes but I'm sure they
could be combined into one?

Router::connect(
'/open-account/:id',
array(
'controller' => 'users',
'action' => 'add'
),
array(
'pass' => array('id'),
'id' => '[a-z]+'
)
);

Router::connect(
'/open-account',
array(
'controller' => 'users',
'action' => 'add'
)
);