If it is the prism unit that fits flush against the glass, there is no way of fixing it. It requires a special bonding process that you will not be able to replicate, and the result will be no good.

I've just had my screen replaced (£706 inc fitting - salient point for all those without glass insurance (I do have it)) and talking to the BMW mechanic he told me that even they can't replicate it at the dealership, only the windscreen manufacturer can fix that.

If it's the electronics that clip onto the bonded prism then you may be able to get them to fit, but it won't be easy (pictures of the problem would be a real help here), and the whole auto wiper/auto lights system then needs re-initialising by the dealer. This again was something the original windscreen repairer could not do. It doesn't take long (about 15 minutes), but it still has to be done in order for everything to work again.

Hope this helps

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Me:
Current: 2011 E71 40D Vermilion Red/Beige Nappa

Wifey:
Current: 2012 R80 Countryman SDX Green/Cream