Add the rum, bourbon, juice, syrup and bitters into a shaker with ice, and shake until well-chilled.
Strain into a Collins glass over fresh ice.
Top with the ginger beer.
Garnish with 2 pineapple fronds and freshly grated nutmeg.
*Coconut-infused rum: Combine 1 750mL bottle of Bluebird Distilling Sugarcane rum and 4 cups flaked coconut in a nonreactive container like a large Mason jar. Let it set for 4 days, then strain out solids through a fine-mesh strainer.