Making the holes would be useless because you haven't got any fitting screws + rotary tool. (https://www.amazon.com/Black-Decker-RTX-B-3-Speed-Rotary/dp/B000MUSLCC i heard this one should be good enough but get a secondary cutting disc)
Get a plastic editing tool like a Dremel with a small cutting disc make a cutout for the fan but make it a bit smaller than the fan so that you can use the screwholes of the fan.