Setting Personal Message in invite box for facebook application through api

Question

Hi, i have an application with the invite functionality which is working fine. Right now i have to manually enter personal message and click send to send the invitation.

But i want a custom message which should be set by api method. I have checked the code but it has parameters:

$params = array();
    $params['api_key'] = FB_API_KEY;
    $params['content'] = '<fb:req-choice url="'.FB_CANVAS_URL.'" label="Check out '.FB_APP_NAME.'"'; // Don't use htmlentities() or urlencode() here
    $params['type'] = $typeword;
    $params['action'] = FB_CANVAS_URL;
    $params['actiontext'] = $actionText;
    $params['invite'] = ($bInvitation ? 'true' : 'false');
    $params['rows'] = '5';
    $params['max'] = '10';
   // $params['exclude_ids'] = $excludeFriendsStr;
    $params['sig'] = $facebook->generate_sig($params, FB_SECRET);

Is there any method for the same?

Please guide me.