The night before, or at least 3 hrs prior to serving, carefully cut all the skin and pith off the pomelo. Cut the segments from the fruit, then heat a non-stick frying pan with no oil on a medium heat. When hot, add the segments in one layer. Let them stick and get a little black (this will take 6-8 mins), then remove from the heat and stir gently to break up the segments. Set aside in the fridge to chill until needed.
To serve, carefully open the oyster shells by holding the oyster in a folded tea towel, flat-side up with the hinge exposed. Insert a knife into the hinge and wiggle to lever open. Discard the top shell and run the knife under the oyster to loosen it from the bottom curved shell. Serve in the bottom shell with 1tsp crème fraîche and 1 tsp scorched pomelo segments. Serve the oysters on top of piles of coarse salt to hold them steady.