This is one reason that I like to book two one way tickets rather than one round trip ticket (except when there is a discount for booking the round trip ticket, such as the VISA 15% off thing mentioned above or the recent Denver 25% off sale).

If you don't have a r/t discount, book two one ways. If you don't show for your outbound one way, it goes back as TTF funds. Cancel before the flight just to be polite. You can do that 1-2 hours before the flight (you obviously are not at the airport, so why not cancel?). You free up space for someone else and your TTF is available immediately instead of waiting 3-4 hours. You can cancel it from your cell phone. If you are in the middle of a meeting or something, you can just be a no show and the money will be available shortly.

Meanwhile, because the return flight is on a separate PNR, there is no way that your cancellation or no-show will have any effect on your return flight. Further, you do not have to call and have the PNR split and you don't have to worry that being a no-show will have any effect on your return flight.