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.
leo @'d me in a thread about his last dream, stating he was passionately making out with a guy he used to know and then woke up while reaching for his crotch, and said that i would "know who 'tf' it is"
and of course i know, it's luke