When pairing a bluetooth keyboard(-like) device with Yosemite, can the pin number be skipped?
You mention a “6 digit number” but from what I understand about how Bluetooth gamepads pair in Mac OS X it should be a 4 digit PIN.

Regardless, you can enter any series of digits from your main system keyboard and it should work. Try something like 0000/000000 or 1234/123456 and it should be able to pair without issue.