Fields with multiple values using views module

I'm working on exposing the data in the signup module to the views module. So far I've got a table view that lists nodes and one user signed up to each node, but it doesn't handle multiple values, i.e. where a node has two or more users signed up.

How do I handle that?

Here's the code I'm using:

/**
 * Hook to expose signup data to views module
 * @ingroup signup_views_api
 */
function signup_views_tables() {
  $tables['signup_log'] = array(
    'name' => 'signup_log',
    "join" => array(
      "left" => array(
        "table" => "node",
        "field" => "nid"
      ), 
      "right" => array(
        "field" => "nid"
      ), 
    ),
    "fields" => array(
      "uid" => array(
        'name' => "Signup: Users",
        'handler' => 'views_handler_field_signupname',
        'sortable' => false,
      ),
    ),
  );
  return $tables;
}

/**
 * Handler to return pretty usernames instead of fairly useless uid info
 * @ingroup signup_views_api
 */
function views_handler_field_signupname($fieldinfo, $fielddata, $value, $data) {
  $obj = user_load(array('uid' => $value));
  return theme('username', $obj);
}