How to reuse 1 php-action for multiple ajax calls with parameters

I’m creating a plugin to build my post types, meta boxes and custom fields. I would like to have auto complete functionality on most of the custom fields. I’ve written the following, that won’t work, but describes what I like to achieve:

function se_wp_head() {?>
<script type="text/javascript">
    var se_ajax_url = '<?php echo admin_url('admin-ajax.php'); ?>';

    jQuery(document).ready(function() {
        jQuery('#cf_label, #cf_band_name').suggest(se_ajax_url + '?action=se_lookup&cf='+jQuery(this).attr('id'));
    });
</script><?php
}
add_action('admin_head', 'se_wp_head');

function se_lookup() {
    global $wpdb;

    $search = like_escape($_REQUEST['q']);
    $cf = $_REQUEST['cf'];

    $query = "SELECT distinct meta_value FROM " . $wpdb->postmeta . "
        WHERE meta_value LIKE ' . $search . '%
        AND meta_key = ' . $cf . '
        ORDER BY meta_value ASC";

    foreach ($wpdb->get_results($query) as $row) {
        echo $row->meta_value . "\n";
    }
    die();
}
add_action('wp_ajax_se_lookup', 'se_lookup');

I insert jQueries suggest functionality for text boxes #cf_label and #cf_band_name in the header and try to send the ID of the actual control where the text is entered to the lookup php function to be a part of my query.

I’d like to be able to have one function that queries the DB with what I type and the control I’m in (the custom field name) to retrieve a distinct list of previous entries. It shouldn’t be that hard, but whatever I try I’m failing, so I definitely miss something..

Hope someone can help. Thanks!