Sorry you're in this situation, but these things do happen sometimes. As I understand it (someone please correct me if this is wrong), if you're upside down then no buyer is going to take over your loan (why should they?). If it's a friend or relative then they might be willing to pay you and wait for the title. Then you can send that money plus the difference to BMWFS and wait for the title. If the buyer is unwilling to do this then you may be stuck. I don't know of any other way around that problem that doesn't involve large amounts of money. (You can't get a bank loan because they'd need the title as collateral. Of course if you have something else you can offer the bank as collateral that would work.)
One thing a lot of people do is take them to a place like Carmax, which is all set up for transactions like this. I've heard they can buy an upside-down car and take your check to pay off the rest of the loan. BUT I've never been real impressed with their offers. I've taken cars there several times for appraisal (it's free and it's a good way to back up a KBB-based estimate because they'll assess body damage, factor in carfax, etc). I really don't recommend this -- you'll get a better price selling it on your own if you can. They recently offered me $14k for my 2007 Solstice (KBB said almost 16), and while they're standing there telling me this there is an identical Solstice -- same year, options, identical condition, identical mileage and even the same color -- not five feet away from me, with a sticker showing $19,900 on the window. You gotta watch those guys. But it is an option and given your situation it may be the most palatable choice.
Incidentally, if you purchased gap insurance it may apply here, covering all or part of the difference between what the buyer pays you and what you owe. Those kinds of policies often cover more than just accidental loss.
You might also want to investigate the cost of shipping the car to your destination. A number of people on this forum have shipped their cars overseas so there is expertise on hand to help you with that. A 135 is well-suited for many overseas locations. It's not like you bought an Escalade.
