Originally Posted by
tomvancouver
You could 'upfare' (on line change my booking, or by calling in) to a fare basis that allows you to use the eups. But for a short flight, it may not be worth the extra cost. The eupgrade website allows you to preview the eup/copay requirements according to the fare class/code. Before proceeding you could make a dummy booking to see if upgrade space exists (within the booking window).
Basic does not allow for upfare. (that's the rule, but I'm sure YMMV if you get an agent who doesn't know or is too lazy to read acpedia)