I am in a similar situation. BMW Financial Services now has a smartphone app promotion, for existing Financial Services customers, in which you set up a test drive, and can receive $300 to $700 off first lease payment, on a car ordered by December 31. I would like to take delivery in mid May and hoping ED will accept an order for delivery 5 months in advance. I thought you could go about 6 months on an existing model, but would appreciate hearing from anyone who has recently ordered that far in advance.
2007 335xi (ED 5/10/07, Redelivery 7/12/07)
2010 335i-xdrive (ED 10/19/09, Redelivery 12/30/09)
2013 335i xDrive (ED 9/15/12), Redelivery 11/23/12) mineral grey
2014 X1 xDrive28 (ED 5/13/13), Redelivery 7/11/13)