Hello,
the requirement to have an original birth certificate ist very strong and I wouldn't await that it will be abandoned. German citizenship is seen as the ultimate step, normally it can't be taken away later, therefore the authorities are much harder than even with Niederlassungserlaubnis (unlimited residence permit). By the way, if your friend already has this unlimited permit, it is a question how he persuaded the Ausländerbehörde to give it: for this you normally also need an original birth certificate. But anyway, the naturalisation (Einbürgerung) is processed by another authority, Einbürgerungsbehörde, and they are even stricter in this point.
If your friend knows the place of his birth, it is perhaps possible to find out, if his birth war registered there. Sometimes people get documents with the help of a special lawyer in their country (the contacts of the lawyers you can ask in the German embassy there). I am only afraid, your friend will have to pay himself for that.
I don't know if it can work with help of the people who can make an official witness of the birth. But as your friend was taken from the country of birth in a very early age, I have doubts that it is possible to find such witnesses.
I think you need an advice of a lawyer who specialises in Einbürgerung. There is certainly much legal practice in such cases, but I have no knowledge here, it is very specific.