Is it really possible? I've already upgraded its BIOS up to current version, but still cannot find it during BT device search in specified menu.
The Apple Bluetooth Keyboard has not been tested yet. However, I suggest you to follow below steps, they describe how to setup a Bluetooth keyboard.
Bluetooth* Keyboards During POST and in BIOS Setup, Article ID: 000016213http://www.intel.com/content/www/us/en/support/boards-and-kits/intel-compute-stick/000016213.html