we are probably on the same page here. on the ones Ive seen all you would need to do is cut a lead that goes to the ribbon cable the the LEDs are on and put a SPST switch on it?
not sure all LED fans use that method though.
That was my take looking at the victim fan I had lying here. Everyday generic Antec labeled fan. The 3 wires fan connector line runs up a small channel to the fan motor. Lifting those wires out and out of the way reveals the pair that go to the foil. Just cut the red (+) and place a simple SPST switch in there and that would do it for a fan like this.