I see where you're coming from, I just don't think it will work. But that could be because I already know how a model car looks/behaves. You may be able to 'trick' somebody who's never seen one though.
Whilst I'm doubtful I would also be interested to see someone's attempt at it.
A further thought:
Your idea may be quite effective under some conditions (e.g. when travelling on the flat), but when falling it wouldn't look right because our model cars already accelerate under gravity in the same way a full-size vehicle does (i.e. in this instance you don't need to slow it down, assuming the track/obstacles are to scale).