Drupal Commerce Change Order Weight at Checkout
You can use HOOK_commerce_fedex_rate_request_alter(&amp;$request, $order) to alter the request before it goes out:
function MYMODULE_commerce_fedex_rate_request_alter(&amp;$request, $order) {
    // Test this value and set it to whatever you'd like.
    $request['RequestedShipment']['RequestedPackageLineItems'][0]['Weight']['Value'] = 1;
    $request['RequestedShipment']['RequestedPackageLineItems'][0]['Weight']['Units'] = 'LBS';
}

Just test the value and update it if you want.