MINI have 'sort of' confirmed that the Sport Button will be available on Cooper from March build, but as yet there is no way to
actually specify it on an order.
Bearing in mind that the people that want a definite 1st March delivery will be having cars built in February, I would be inclined to ask your dealer to postpone putting your order through to MINI until you know for sure. Worst case scenario it won't be available and you'll get a March build slot for April delivery.
This will of course mean you will have to be ultra switched on in terms of keeping up-to-date with changes to the options list, as it is not beyond some dealers to just order your car anyway and tell you it isn't available.
(Did I say that out loud again?
)