I'm wondering why you would make all the payments up front? You're not really saving any money, you just get out of making payments every month. Better to invest your money (short term) and pull it out and pay for the second year later. And if you have that much cash to burn then by all means just buy the thing...or I'll send you an address in case you need a place to store it
I wouldn't go 2 years on a lease. The payments are calculated by taking the selling price minus residual value (after the period and mileage), adding financing charges onto that and dividing over the period. So, since most of the car's value is lost during the first 12-18 months, extended in the lease to 36-48 month (while the car is still covered by BMW) makes a little more sense.
The only up side I can see on a 2 year lease is if the true aftermarket value is greater than the financing companies (BMW Financial for example) estimate. I actually made money on a Mini CooperS (don't ask, my wife's idea...). I sold it back to a dealer at lease end and they wrote me a check for the difference (around $1800 or 4 month's of payments and a tax credit on my 335i). So if the car is worth that much more than payoff at 2 years you could get out of the lease and sell the car and recover some of your payments. If you are in IL or TX, and try to sell it to a third party then you'll have to pay sales tax on the buyout figure. Sell it to a dealer and that problem goes away, but you're also not getting the most for the car. You can generally make that up in tax credit towards a new car...I did.
Hope that helps.