Provide more specific information to piwik. eg user ID

Hello guys,
dows piwik support this in any way? I have a closes system, where users have to log in. and i want use piwik to track the user log ins. is that possible? can i generate the part of javascript, which has to be added with a php script eg.

piwik_action_name = 'UserName: mojo';
piwik_idsite = 1;
piwik_url = pkBaseURL + "piwik.php";
piwik_log(piwik_action_name, piwik_idsite, piwik_url);

thank you!
meanwhile i will take a look on the api, maybe i discover something style_emoticons/<#EMO_DIR#>/smile.gif