Usually wings have root (or end) ribs that are glued together at the center. It would be difficult to make a hole for the leads in them. What I have done on similar planes is to cut/drill two holes, one in each wing just outboard of the root ribs. Make sure they will be insde the fuselage! It's easier to do this before the wings are joined because usually you can see the servo lead tubes (or openings in the ribs) from the ends. You can then line up the holes you will make with these.

If you fiberglass the center section, just cut through the glass with an xacto knife after the resin/epoxy cures. You will be able to see the holes.

It will make things easier later if you install servo lead tubes in the wings. If you have to change the leads for some reason, or if you switch radio equipment form plane to plane, it will make it easy to snake the leads through the wings for re-installation. The tubes can be made from rolled paper and tape! Cheap and easy. Or you can get cardboard ones at the hobby shop. Of course, this needs to be done before you join the wings.

Hope this helps.

Dave