Adding values to an existing Session array

[eluser]BrandonDurham[/eluser]
I am creating a session array called "entry_data" and filling it with a few values, like this:

Code:

$entry_data = array(
    'album_title' => $this->input->post('album_title'),
    'release_date' => $this->input->post('release_date')
);
$this->db_session->set_userdata('entry_data', $entry_data);

How do I go about later adding more values to the $entry_data session array without overwriting the data that's already there?

Thanks!