no, this is not possible, it would not start your car. There is a transponder chip within the key that communicates with the car's EWS (immobilizer). It is not possible to replicate the random code the key and EWS generate. Keys for your car can only be bought from your main dealer and you must provide proof of ownership and id when ordering your key.
I know it is possible for non-BMW cars. It did it for my Saab 9-5 where you program the car to recongnize new remotes and transponders. It also seems to be more logical this way - I imagine it may be very hard to program a transponder chip.
So I need some more elaborate answer explaining why it is not possible for MINIs.
Your Mini has the same immobilization system as the E46 3-series BMW. This is called the EWS system. The EWS control unit installed on your car is matched to 10 keys stored on file at the factory. All the keys are ordered to the chassis number of your car via your main dealer. The EWS control unit is paired to the engine management control unit of your car, so without a recognised key the EWS control unit does not send the appropriate coded signal to the engine management to enable the engine to start.
Afterall, what good would an immibilizer be if you could just code your own keys to it?
If I had that information I would be an incredibly wealthy man. When I say that each EWS is programmed for the 10 keys, that is all they are programmed for. For example, if a customer managed to loose all 10 of these keys then the EWS control unit would need to be replaced and the old one would literally only be good for the bin.
I see the adverts on eBay for BMW and MINI keys and they're very clever as word the description such that it doesn't at any point say that it will be able to start the car, and there's a good reason for that. I also see people bidding on second hand keys, which is only a good idea if you knew where the car that the key matched was kept at night and you were intending to steal it, otherwise it's just an ornament.
I have personally been to the main parts dept and seen the room that the keys are made and it would literally put Fort Knox to shame. This isn't a second rate immobilizer system from a local tuning store, this is a BMW system that they spent years and millions of Euro perfecting.
I urge you not to waste your money on any key you might find online and buy a genuine key from your dealer.
Sorry but I cannot accept your answer. You just say it cannot be done without good explanation why. Also, I see information suggesting the opposite on variuos sites and forums. For example: