I am afraid you are probably going to have to supply some script on this. Never rely on the finger id. If you are tracking touches, always track the current finger id.
i am not using the fingerid in the game,
But there is bug saying, touch is not working in the game when it is goes background for 32 times ( by showing ads, moreapps or home screen )
I just kept log to see what is happening
foreach(Touch touch in Input.touches)
Debug.Log("count = "+Input.touchCount+"touch id = "+touch.fingerId);
count variable is returned properly but fingerid keep increasing after game going background.
once the fingerid reaches 32 , nothing in the game is touchable.