So, what I’m thinking… use a hacksaw and cut the Noctigon 32mm at 3 points, dividing it into thirds. Done properly, the 3 pcs should now line up and allow use of this reflector. Traces can be rejoined across the gap with flat sheet material. 
Could either solder them back together or leave them apart, glue the individuals down to the emitter shelf using the reflector as a template to position them perfectly.
Probably as easy or almost as easy as fitting 3 16mm Noctigons and then messing with all the wiring.
(Cut on the downstroke only. Pulling a backstroke would lift traces off the mcpcb.A band saw would make this easy peasy.)