As mentioned, you can't emulate an analog stick with a single state digital input, like a keyboard.
What you are going to get is basically an 8-way joystick, rather than an analog one.
Any solution you find to work around using their proprietary hardware is likely going to be more expensive than the gamepad that EA is selling.
(i.e. if you get an arcade analog stick, and an AKI or A-pac, you are probably looking at a minimum of $50--without any buttons for it).