Talk to an Owner Advisor. They can keep an eye out for you to get an inventory car when one comes up matching your spec.
The big discounts are only when they change the price book, for the most part. There were big discounts on the X when the PUP was changed to all inclusive last July, for instance. If you were missing one of the options on an inventory car there was a pretty good discount. There was also a hefty discount on the 90D at the end of life, so if a bigger battery gets announced you can take advantage of that time to get a good discount.