Using iTween for a race ?

I've seen this question posted at to a certain extent, but not related to what I'm specifically trying to achieve.

I'm trying to create a simple race between few gameObjects, each one following it's own spline. Splines are more or less equal in distance, but each one is tweaked to give the impression that each object is following it's desired way. Perhaps a single spline with some random offset will be smarter ?

I've been playing with the function MoveTo and the callback OnUpdate, but I seem unable to accomplish my goal. The idea is that I want to set on start the final position of each gameObject. For that I should affect, during the animation, the speed or time parameter to make some of them accelerate or slow down so some "race coordinator" can play with the values so each object will arrive to finish line in the required order ?

Can someone point me in the right direction to accomplish this ?