The dihedral of the Storch wing will make using a carbon spar or other straight, rigid rod difficult. If you have woodworking tools you can cut a short section of wood (like a paint stick) into the "V" shape of the wing and laminate the front and back of the foam spars. You can use a carbon rod or arrow shaft to reinforce the straight sections of the wing.
That being said, my Storch is several years old and I haven't folded the wings on it yet, and I built it without any modifications. I also don't try to do crazy acrobatics with it. :-D