如何修改attribute模組增加複選功能

這個模組提供一種屬性或是附件的選擇到商品節點,目前的顯示功能只有選擇框、單選按鈕及文字欄位,我想增加一個複選框需要修改程式碼,不知道有哪位程式高手可以幫我看看要寫在哪?該怎麼寫?
那一段的程式碼如下:
function _uc_attribute_alter_form($product) {
$nid = intval($product['nid']['#value']);
$qty = intval($product['qty']['#value']);
if (!$qty) {
$qty = 1;
}

// If we were passed an actual node object...
if ($node = node_load($nid)) {
// Load all product attributes for the given nid.
$result = db_query("SELECT * FROM {uc_product_attributes} WHERE nid = %d ORDER BY ordering", $nid);
$priced_attributes = uc_attribute_priced_attributes($nid);

// Loop through each product attribute and generate its form element.
while ($relation = db_fetch_object($result)) {
$attribute = uc_attribute_load($relation->aid, $nid, 'product');

// Build the attribute's options array.
$options = array();
foreach ($attribute->options as $option) {
switch (variable_get('uc_attribute_option_price_format', 'adjustment')) {
case 'total':
$display_price = in_array($relation->aid, $priced_attributes) ? ', '. uc_currency_format(($node->sell_price + $option->price) * $qty) : '';
if (count($priced_attributes) == 1) {
break;
}
case 'adjustment':
$display_price = ($option->price != 0 ? ', '. ($option->price > 0 ? '+' : '') . uc_currency_format($option->price * $qty) : '');
break;
case 'none':
default:
$display_price = '';
break;
}
$options[$option->oid] = $option->name . $display_price;
}

if (count($attribute->options) && $attribute->display > 0) {
if ($attribute->required) {
if ($attribute->display == 1) {
$options = array('' => t('Please select')) + $options;
}
unset($relation->default_option);
}
$product['attributes'][$attribute->aid] = array(
'#type' => $attribute->display == 1 ? 'select' : 'radios',
'#title' => $attribute->name,
'#description' => check_plain($attribute->description),
'#default_value' => $relation->default_option,
'#options' => $options,
'#required' => $attribute->required,
);
}
else {
$product['attributes'][$attribute->aid] = array(
'#type' => 'textfield',
'#title' => $attribute->name,
'#description' => check_plain($attribute->description),
'#default_value' => $attribute->required == FALSE ? $attribute->options[$relation->default_option]->name : '',
'#required' => $attribute->required,
);
}
$product['attributes']['#theme'] = 'uc_attribute_add_to_cart';
}
}
return $product;
}

// Returns an array of display types used as options when creating attributes.
function _uc_attribute_display_types() {
return array(
0 => t('Text field'),
1 => t('Select box'),
2 => t('Radio buttons'),
);
}
我修改了好幾次都失敗囉....