In a bowl mix together the creme fraiche, heavy cream, 2 tablespoons of the caviar, lemon juice, and chopped chervil or dill. Refrigerate the sauce for 1 to 2 hours before using.
Just before serving, cut the salmon into 12 pieces; they should be large enough to wrap the oysters into roughly square little packets. Wrap the oysters.
Divide the cream sauce among the serving plates, creating a pool of sauce at the center of each plate.
Divide the wrapped oysters among the plates, arranging them on the sauce pools. Garnish each packet with a generous 1/4 teaspoon of caviar and a chervil or dill sprig.