I hate to tell you this but, that's not going to work.
You could easily achieve everything you want to without phantom markers. It makes me worry but I'm not going to go any further on that subject, rather, I'll just tell you how to achieve your goal.
Save the replay past T1, watch the MPH during the replay, find the top number before the first real turn, then find the bottom number during the first turn. That alone will give you how fast a car can go through the turns as well as how fast it runs at the top of the hill.
The problem with that is... The sector time is secondary to the feel. 👍
Well... Back to the game for me.