Pass fees from one shipping method to another - magento

Question

I have a tricky shipping issue that I'm trying to work out. I have a custom extension that calculates the table rates for all of the domestic shipping. But for international, one type of product(category A) is a flat $35/product shipping fee and the rest of the products (categories B and C) are calculated by UPS and USPS. The only way I've been able to figure out how to properly calculate shipping if a customer purchases both types of products is to create a table rate for Category A, then pass it along to UPS/USPS as a handling fee. Is there a variable/method I can use for this process? I haven't yet found one.
As requested, here's my function:
public function collectRates(Mage_Shipping_Model_Rate_Request $request)
{
// Cut out code where it adds up the categories and the number of items in each category
$rates = $this->getRates($request, $_categories);
if (!empty($rates))
{
$rateTypes = array();
foreach($rates as $rate)
{
$rateTypes[] = $rate['method_name'];
}
$rateTypes = array_unique($rateTypes);
$i=0;
// Create array to pass along to UPS/USPS, if needed
$tempCategories = $_categories;
foreach($rateTypes as $rateType)
{
$groupPrice = 0;
foreach($_categories as $category=>$catQty)
{
$rateExists = false;
$standardRate = 0;
foreach($rates as $rate)
{
$rateCats = explode(',',$rate['category_list']);
if(in_array($category,$rateCats) && $rate['method_name'] == $rateType )
{
$rateExists = true;
if($rate['condition_type'] == 'I'){
$ratePrice = $rate['price'] * $catQty;
}
else if ($rate['condition_type'] == 'O') {
$ratePrice = $rate['price'];
}
unset($tempCategories[$category]);
}
else if(in_array($category,$rateCats) && $rate['method_name'] == "Standard" && $rateType != "Standard")
{
if($rate['condition_type'] == 'I'){
$standardRate += $rate['price'] * $catQty;
}
else if ($rate['condition_type'] == 'O') {
$standardRate += $rate['price'];
}
unset($tempCategories[$category]);
}
}
if($rateExists == false)
{
$groupPrice += $standardRate;
}
else
$groupPrice += $ratePrice;
}
if(count($tempCategories) > 0)
{
// Figure out how to pass the $groupPrice to other shipping methods here
}
else {
$method = Mage::getModel('shipping/rate_result_method');
$method->setCarrier('shippingcodes');
$method->setCarrierTitle($this->getConfigData('title'));
$method->setMethod('shippingcodes_'.$rateType);
$method->setMethodTitle($rateType);
$method->setPrice($groupPrice);
$result->append($method);
}
}
}
else
return false;
return $result;
}