The exoskeleton of crustaceans does not contain calcium, but does contain chitin, a substance similar to keratin. This same material that makes up your fingernails and is not digestible. It could possibly cause in impaction if the frog would to ingest too much of it, so I would skip feeding the shrimp skins. To give him extra calcium you can make of a slurry using water and a fine calcium/vitamin D3 supplement. You will need a blunt syringe to inject the slurry in his mouth. Some pet stores carry them and so do some hardware stores, just look in the adhesive aisle. You could get medical grade blunt syringes from a vet.
I usually start by putting some of the powder into the syringe, then insert the plunger, pressing the air out of it. Then I draw in water to the syringe, shaking it to mix the water and powder up. Then into the frogs mouth it goes. I would give the slurry every other day.
Remember MBD does not go away over night, so be patient.
Also when putting them outside, monitor the tempertures and dapple the sun light that the frog is getting. Direct may sunlight may be too much to handle, especially in the begining.