I haven't done it myself, but it seems to me that the only thing causing this is that the tail surface is made of thick foam, hinged at the top, with a straight cut. If you could carefully "V" out the cut, I think the flaps would have room to go down, provided the rubber band is tight enough to pull them down.

If you accidentally cut the hinge, clear packing tape will provide a good repair.

But bear in mind, a little up elevator through the turns is customary to keep the plane from diving.