Possible, but poor solution. They really need to come up with something more elegant... like a nunchuck ripoff.
Is it worth it though, as a stopgap from just using a second wand in left hand?
After all this monoshock should still have a rechargeable battery, possibly rumble, an analog and/or a dpad, 2 to 3 buttons, BlueTooth, USB... how much cheaper can it be than a dualshock or an extra wand, and how much value would it seem to offer when compared to controllers you can actually use by themselves in other games?
I don't think I would buy one for $30, maybe the value perception is the downside to announcing and producing such an obvious and easy piece of engineering.