Can I get payment authorization in excess of order total? - authorize.net

[idc1]

I am using ZC 139 with the built in Authorizenet AIM module. Because of drastic differences between weights and sizes of products being shipped, it is hard to do a flat rate shipping fee, % of weight, or any other simple formula to come up with an accurate shipping rate. So the way we leave it is that actual freight will be determined once the package has been picked and processed.

What is the best way to set up similar to gas stations? I know capturing more than what is authorized is NOT doable. Therefore my idea is to get authorization from authorize.net for cost+$20 (or some reasonable amount). This way we can go back and then capture cost+$12.17 once the package has completely been processed.

So I'm taking a stab in the dark, within inc/modules/payment/authorizenet_aim.php

can I insert something like 'x_amount' => number_format($order->[info['total'] + 20], 2) into the below:

    // Populate an array that contains all of the data to be sent to Authorize.net
    $submit_data = array(
                         'x_login' => trim(MODULE_PAYMENT_AUTHORIZENET_AIM_LOGIN),
                         'x_tran_key' => trim(MODULE_PAYMENT_AUTHORIZENET_AIM_TXNKEY),
                         'x_relay_response' => 'FALSE', // AIM uses direct response, not relay response
                         'x_delim_data' => 'TRUE',
                         'x_delim_char' => $this->delimiter,  // The default delimiter is a comma
                         'x_encap_char' => $this->encapChar,  // The divider to encapsulate response fields
                         'x_version' => '3.1',  // 3.1 is required to use CVV codes
                         'x_type' => MODULE_PAYMENT_AUTHORIZENET_AIM_AUTHORIZATION_TYPE == 'Authorize' ? 'AUTH_ONLY': 'AUTH_CAPTURE',
                         'x_method' => 'CC',
                         'x_amount' => number_format($order->info['total'], 2), 

[idc1]

It seems as though the solution is as simple as inserting +20 no additional [] or () needed.

'x_amount' => number_format($order->info['total'] + 20, 2)