Answer Wiki. The system would be cued off the pilot's helmet, so it will definitely look where your head is pointing, not your eyes specifically (that would be a gaze-tracking system, which AFAIK hasn't yet been used for this kind of application).
Exercise to Gain Leg Weight. Although you can't make your body gain weight in your legs, you can perform exercises that encourage the growth of leg muscle. Squats, lunges and step-ups are examples of such moves that target the legs and recruit a lot of muscle fibers for growth.
When you gain weight, fat doesn't just accumulate in your legs, so spot training your legs will not slim them down. To lose leg fat, you must decrease your total body-fat percentage, and the fastest and most effective way to do this is by consistently burning more calories than you consume.