etivite :: \ē-'ti-və-tē\

//if a new group is created - attach an admin, mod, demote
function my_group_autoadd_admin( $args ) {
    global $bp;

    //args is the group_id
    if (!$args)
        return;

    if ( !is_site_admin() ) {
        //use this section to demote the creator to a mod - assuming the logged in user is creating
        $member = new BP_Groups_Member($bp->loggedin_user->id, $args);
        $member->is_admin = 0;
        $member->is_mod = 1;
        $member->user_title = __( 'Group Mod', 'buddypress' );
        $member->date_modified = gmdate('Y-m-d H:i:s');
        $member->save();
    }

    //use this section to add some user_id (from wp_users->ID) as an admin
    $member = new BP_Groups_Member(INSERT_THE_USER_ID_HERE, $args);
    $member->is_admin = 1;
    $member->is_mod = 0;
    $member->user_title = __( 'Group Admin', 'buddypress' );
    $member->is_confirmed = 1;
    $member->date_modified = gmdate('Y-m-d H:i:s');
    $member->save();

    //use this section to add some user_id (from wp_users->ID) as a mod
    $member = new BP_Groups_Member(INSERT_THE_USER_ID_HERE, $args);
    $member->is_admin = 0;
    $member->is_mod = 1;
    $member->user_title = __('Group Mod', 'buddypress');
    $member->is_confirmed = 1;
    $member->date_modified = gmdate('Y-m-d H:i:s');
    $member->save();

}
add_action('groups_created_group', 'my_group_autoadd_admin', 1, 1);

If you have no need for the BuddyPress Restrict Group Creation plugin here is the function I used to demote the creator and automatically assign an admin and/or mod to the new group.

Notes:
Replace INSERT_THE_USER_ID_HERE with the corresponding user_id

Tested on:
BuddyPress 1.2.4.1
WordPress 2.9.2/3.0