That's what Dremel tool plunge router bits are for. Tape a piece of ply with a rectangular opening the size of the servo on the center section of the wing and route away.

Almost all the Bridi Kaos designs are built the same way. Usually a thick slab fuselage top which is pinned down on the board; the fuselage is then built upside down onto the slab top.

As Jim said, a wing jig (the Great Planes jig is about $19) is great for building the symmetrical wing halves.

They are very straightforward, but if you start a build thread people here can guide you through it.

David