A resistor won't do the job for you, the fan controller is expecting a pulse train, not a steady DC voltage.
I'm not familiar with your particular motherboard, but I have seen other boards that had an option in the BIOS to disable CPU fan warnings.
Can't think of any viable ways to "fool" the BIOS into thinking that there is a fan attached.
BTW - your user name makes me think of the TV series Adam-12 from many years ago. Radio: "2-11 in progress, 1-Adam-12 handle code 3."