Your astute financial skills are quite flawed. Yes you could dump the car for less than the remaining payments, but you then would have NO CAR......
A large down payment on a lease is NEVER a good idea - regardless of your intentions. If the car is stolen or totaled, (GAP insurance is irrelevant), you're not a check back from LEXUS for your downpayment.
If you want to bring your monthly costs down, Lexus offers a MULTIPLE SECURITY DEPOSIT option (in most states), which allows you lower the interest rate and thus lower the monthly payment. This is a much better option.