I don't see why it wouldn't work. I have always used barrel pads for training purposes. I've found that they definitely help save your horse's back. I'm an equine massage therapist, and I see more sore backs from poor or non-existent saddle pads that I care to count.
I'll usually tell my clients to switch to a thicker or better weight-distributing pad. Generally this suggestion is met with a look of horror and I'm informed that, "It won't look good," or, "My horse won't be able to feel my subtle weight shifts."
At that point, I always feel like informing them that I've seen them ride, and you're better off if your horse can't feel your "subtle" weight shifts. Or, your horse feels nothing but pain now, so...I've learned to keep these comments to myself, however. Also, if I suggest that their horse could benefit from some time off to let the soreness go away, the usual response is, "But I have a trial coming up. I have to keep riding him."
if you REALLY want the best investment for your horse's back, go to: www.TheAlpacaHorse.com and buy one of their 100% organically produced hand-woven alpaca saddle blankets.And they are made entirely from New England raised alpaca fleece and hand-loomed in Connecticut. I have 2 of them and my dressage horse has never gone better !