Buy the JST plug with the right pin pitch (in your case 2mm), and grind it so it fits. You can find male to female cables, so you also don’t have to modify the original connector on your noctua fan.
One possiblity would be to cut the original cable and add a new connector to both sides. A female one to the one that goes to the board, and a male one to the one on the fan.
That way you have all the original parts still there, but you can use the one part of the cable as an adapter.