Compound-Curved Wing Tips

Pou du Ciel has interesting compound-curved wing tips, how does one go about fabricating it?

Foam Wings

1. Trim the airfoiled foam blanks to planform and sand the wing tips to profile.
2. Make a wing tip jig to each tip curvature, marking on the jig the planform of the wing tip. A concave jig is better than a convex jig because it is easier to push at the centre then simultaneously at both ends, and in the case of foam wings, easier to see and sand the saw cuts of step 3.
3. Saw 3/4 of the way through each rib position. Offer up to the wing tip jig, if the saw gap is insufficient for the curvature, sand with knife file.
4. Bend and cyano. 
5. If the 2 pairs of wings are to be covered with tissue, then I'd say that they are sufficiently reinforced.

Built-up Wings

1. Do up left and right wing tip jigs as per step 2 under 'Foam Wings'.
2. Cut the shape of wing tips in 5mm foam, undersize them to allow for the thickness of the leading and trailing edges. 4 will be needed, one for each wing because I observed that the wing chord of the rear wing is shorter than the front wing's. These are our wing tip formers.
3. Bend and glue the wing tip formers to the wing tip jigs.
4. Soak 4 or 6 or more 1/16" square strips in water.
5. Ease the strips into position against the wing tip former and on the wing tip jigs.
6. Starting at the base and going towardes the tip, spot cyano the strips together.
7. Excess to be trimmed off.

Then again, the tip proposal for built-up wings seems to be too much work and over complicating.

If the spars are made with the curved dihedral, why not just do up a normal tip? So long as the wood sections are small enough, they should be able to be nudged into position. Any cracks, just fix it with CA.