Not a good idea. You'd only be able to use the extender for such small periods of time (maybe 10 minutes) that it just would not be effective at all since that's no time to build and maintain tension. Trying for longer than 20 minutes could just lead to serious issues since you'd be blocking off blood flow through the penis for far too long. Stick with using an extender the way it was designed to be used.
i've been doing it for two days and it feels great. Obviously you can't extend the thing as far as you normally can but it feels great and my PI's are higher than when i put the thing in straight up so i'm gonna continue doing it once or twice a day with my normal routine.