You make the deal when you come to sell it/trade it in when the time comes.
Believe me, it is much, much better to have a car with low depreciation and get no discount when buying than to get a huge discount when buying and be faced with equally huge depreciation.
With a huge amount of time and effort and some luck (i.e. someone with a sales target to meet that day), you may get a couple of hundred off a new Mini, but I wouldn't count on even that.
I'd just take a deep breath, pay list and be thankful you've got one of the better deals going (come time to sell it).
Bottom line is that new Minis, even at list price, are one of the better deals going.
By the way, if you can wait, you may as well spec it exactly the way you want (and there's a huge choice), as you'll be paying list even for cars in stock that mightn't be exactly what you'd like.