Yes it is possible, the standard rails will unbolt (you may have to break some plastic covers to access torx bolts) but there are new parts that aren't immediately obvious - like the different shaped storage cover (load area carpet / reversible cover) - which are very expensive.
Take a look at Realoem section 51.47 - you'll need rails, lashing eyes, a new floor and handle - look at everything that gets replaced with option S439A
http://www.realoem.com/bmw/enUS/show...diagId=51_8212
I considered this but gave up as far too expensive and ordered my new X3 with S439A - mainly because I wanted the extra glove compartment under the light switch
However, I'm not impressed with the S439A lashing eyes or rails - the eye is made of very thick metal and the BMW nets wont hook on to them. You also can't position an eye at the very back of the rails - exactly where the nets and the plastic load liner are designed to work with the standard set-up.
I'd stick with what you have and go for an external bike carrier - I use a thule 3 / 4 bike carrier mounted on the tow ball or thule roof-mounted carriers