the snippet is available by going to window -> Snippets.
in the snippets window go to eCart -> Shipping -> FedEx Sevices to add the services list to the checkout page:
<select name="FedEx_Service" id="FedExService">
<option value="PRIORITYOVERNIGHT" selected>Priority Overnight</option>
<option value="STANDARDOVERNIGHT">Standard Overnight</option>
<option value="FIRSTOVERNIGHT">First Overnight</option>
<option value="FEDEX2DAY">FedEx 2 Day</option>
<option value="FEDEXEXPRESSSAVER">FedEx Express Saver</option>
<option value="INTERNATIONALPRIORITY">International Priority</option>
<option value="INTERNATIONALECONOMY">International Economy</option>
<option value="INTERNATIONALFIRST">International First</option>
<option value="FEDEX1DAYFREIGHT">FedEx 1 Day Freight</option>
<option value="FEDEX2DAYFREIGHT">FedEx 2 Day Freight</option>
<option value="FEDEX3DAYFREIGHT">FedEx 3 Day Freight</option>
<option value="FEDEXGROUND">FedEx Ground</option>
<option value="GROUNDHOMEDELIVERY">Ground Home Delivery</option>
<option value="INTERNATIONALPRIORITY FREIGHT">International Priority Freight</option>
<option value="INTERNATIONALECONOMY FREIGHT">International Economy Freight</option>
<option value="EUROPEFIRSTINTERNATIONALPRIORITY">Europe First International Priority</option>
</select>
after adding the services list to the checkout page, open the confirm page, near the bottom, there is a collection of hidden form elements, add another one with the same name as the services list, to capture the value posted by the checkout page:
<input name="FedEx_Service" type="hidden" id="FedEx_Service" value="<?php echo((isset($_POST["FedEx_Service"]))?$_POST["FedEx_Service"]:"") ?>" />
then add a set session value behavior, go to the server behaviors panel, click the plus button and select eCart -> General -> Set Session Value for the trigger, select any form post.
set the name to FedEx_Service for the value, click the lightning bolt and select the FedEx_Service form element.
in the fed ex server behavior, bind the servicer setting to the FedEx_Service session variable.