You don't have to attach the lens to the leading edge, as you sussed out, you make a frame for it with nut plates.
Here's how they did it for Cubs and other Pipers - make a false nose rib, and attach it to the spar the length of the light fixture away from a true rib. Rivet a half inch wide strip along both (.020 works great), and then tag another across top and bottom. You can cheat some strength in there by placing K1000 nut plates in the corners where each ear is on a different part, too. Also, cut two pieces of aluminum sheet that match the the airfoil of the nose rib and, after painting black, rivet to the sides of the ribs to keep the light out of the wings and going forward.
The real stunt is making the measurements to cut out the light fixture hole in the leading edge material. One wants to be shy to the fixture, as it's always easier to cut more off of a hole.
(I had to do this at work last month)