Whisk or shake together the rum, cream of coconut, pineapple juice, triple sec and nutmeg until well combined (see Cook's Note). Chill for at least 2 hours.
Meanwhile, cut the stem off the pineapple. Using a pineapple corer, twist into the top of the pineapple but don't cut all the way through to the bottom. Pull out the pineapple rings and reserve for drink garnishes. Use a paring knife to cut away as much of the remaining core in the pineapple as possible. Insert a fruit keg tap into the pineapple following the manufacturer's instructions. Replace the stem on top of the pineapple like a lid and refrigerate until ready to use.
Shake the chilled drink vigorously. Pour through a fine-mesh strainer into the hollowed-out pineapple.
To serve, pour about 1/4 cup of the drink mixture over ice in a glass and top with some pineapple soda. Garnish with a pineapple ring and serve.
Shaking the drink in a resealable plastic quart container works well.
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