This is probably not what you're looking for but I'll mention it anyway. You can calculate or lookup the angle of attack given the airspeed, altitude change and throttle setting. Assuming it's constant for a few seconds. Simpler when altitude is unchanging. Every model is different depending on the wing configuration and shape. You would have to sample a few points experimentally first to make a table. Isn't the end result the same as measuring it directly? During level flight, this method would be much more accurate. Isn't this the circumstances you want to measure?