Yes that's what I've done as well. Look for approved used cars from BMW with all the kits that you want, then buy it. I reckon by doing so you are saving a lot of money, as a full external MP body kit with wheels costs around 6000pounds!!
Sometime it's worth calling the dealership and ask if they can release the car earlier as my understanding is that the dealer has to keep the car for 4-6 months before they can sell it.
I've got mine at 3 months and only 1500miles on the clock
One thing tho, make sure you check with the dealer whether the MP exhaust is installed as you can't tell from the pic in BMW website and it is also not clear from the car description.....