Acer Aspire one FN(function) key HELP PLEASE

Hello,
I was wondering if anyone knew how to use the fn key without the actual aspire one keyboard. I am making a custom computer for a specific application and I don't have the keyboard connected. Is there any way to map the function key to something in os x, or perhaps on the os x virtual keyboard? I would like to be able to control the screen brightness from within os x instead of using the physical aspire one keyboard. I think there is the app called shades but I don't think it controls the hardware brightness like the fn key. Thanks!