7 – How to pass theme variables in #theme in a form element?

I need to pass product variable defined in hook_theme() and invoked in #theme
but not sure how to pass product variables in #theme
Please suggest.

    function storeinv_theme() {
      return array(
        'storeinv_pickup' => array(
          'variables' => array('product' => NULL),
        ),
      );
    }

    function storeinv_uc_product_description($product)      {
      $description = array(
        'pickup' => array(
          '#product' => array(
             '#type' => 'value',
             '#value' => $product,
           ),
           '#theme'  =>'storeinv_pickup',
           '#weight' => 1,
         ),
      );


       return $description;
}

    function theme_storeinv_pickup($product){

            $data = $product('#value')->data;

            if (isset($data('pickup')('store_id')))
            {
                    $store_id = $data('pickup')('store_id');
                    $day = $data('pickup')('day');
                    $date = date( 'l m/d/Y g:ia', strtotime( $day ) );
                    $result = views_get_view_result('field_altstoreid_value','default');
                    foreach($result as $k => $v){
                      if ($store_id == $v->field_altstoreid){
                            $name = $v->title;
                            return "<p>Pickup " .$date."at " . $name." </p>";
                      }
                    }
            }
            else {
                    return '';
            }
    }