Hi, this is a relatively easy and straight forward task. If you take the beak off (about a 10 min job) you will see the drilling points under the beak. There are two squares with a circle in each for the size of hole required. You will also notice 2 lugs on either side of the frame that the beak fits to where the screws that fix the winglets on attach to. If I recall the clips for threading the screws into are not there but cost a few pence from BMW or get them from Halfords.
If you buy the winglets from Nippy Normans they come with a template BUT I would recommend the method above as you need to get the holes and the lugs to line up perfectly. Fairly simple job.
Hope this helps.