This is hardly an uber realistic option, but could be something a few people with just 2 pedals (like myself) might like the idea of at least:
Perhaps for the starts you could have the option of using the brake pedal as the clutch. So you declutch by pressing the brake pedal to the floor, select first gear with your paddle, and then when the lights go green you launch the car by applying the throttle and at the same time releasing the brake pedal as you would a clutch pedal. Then when you have fully released it, or grabbed the next gear, the clutch becomes automatic and your left pedal becomes the brake pedal again. Obviously something would have to hold the car still if the grid were on a slope, and that would have to be automatic or wheel operated, but I can't see any other obvious problems, don't think i've often had to brake before even getting into 2nd gear.
Would at least be a more involving way of getting off the line, though perhaps not something everyone would take to. I think I'd find it more realistic than just hitting the paddle to engage 1st gear after the lights go green, no racing driver will still be in neutral when the first red light goes on, never mind when they go out.