Oh so you did make a loss.
Lol yeah gotta love the internet,I interpreted "without loss" as meaning "without loss".
That said though I do now know that you mean balance it out in the event of a sale without having to pay over and above monthly payments up to date,makes sense.Your example is pretty easy though as the polo GTI is relatively cheap and it holds value due to image/demand.So I see how you're thinking this through,much better than most people would(for example people who buy a Renualt new,lol.)
What were your other cars?
For me unfortunately I doubt that would work very well for a discovery 4 or X5.Bigger cars tend to depreciate quicker and you always loose out buying new on finance.