I tested this on 1.9 and you might put this code into a helper but if you look at the code which gets the associated products it eventually calls Mage_Catalog_Model_Product_Type_Grouped->getAssociatedProducts()
The code below sets the order by price and descending.
$_product = $this->getProduct();
$_grouped = Mage::getModel('catalog/product_type_grouped');
$_storeFilter = $_grouped->getStoreFilter($_product);
$_status = $_grouped->getStatusFilters($_product);
/** @var Mage_Catalog_Model_Resource_Product_Link_Product_Collection $_associatedProducts */
$_associatedProducts = $_grouped
->getAssociatedProductCollection($_product)
->addAttributeToSelect('*')
->addFilterByRequiredOptions()
//->setPositionOrder()
->addStoreFilter($_storeFilter)
->addAttributeToFilter('status', array('in' => $_status));
// Add custom filtering here
$_associatedProducts->setOrder('price', 'DESC');