i wouldnt bother mate, the roof rack boat has sailed, and is currently docked up at no-mans land harbour along with the good ship 'bad boy bonnet', the tanker 'whale tail spoiler' and the speedboat named 'flip paint'.
having said that, i bought an american roofrack for my 5 several years ago, which didnt use the guttering...you had to drill into the roof! - needless to say i never fitted it and sold it to a mini owning mate....
looked abit like this: (but with wood effect vinyl sticker down the side)