You can lay on your back with your legs apart up against a wall, and just read a book or listen to music and sit like that. The gravity will gently pull your legs down and stretch them. If you do this every day your legs will stretch further and further. You'll have to practice the other ways also, but this speeds the process up tremendously.
If speed and time are of the up most importance. You could tie two ropes to your ankles then tie each of the ropes to two different car bumpers going in opposite directions, Good luck! This probably won't end well.