Step 5: Mise en Place
Cut your strawberries, kiwi, and cantelope into long, thin strips for inclusion in the roll. Stage these pieces in small bowls. Cut the watermelon into slabs that are about the same size as the slab you'd find on hand-formed sushi.
Take your modelling chocolate out of the fridge and break into one large piece and one smaller piece. For each bit of the chocolate, knead it a bit to make it pliable, then roll it between pieces of parchment paper until you have a thin, squarish sheet. Stash chocolate in the freezer for a minute or two if it starts to get too warm to work with, and stash it in the freezer for about 5 minutes before making the final roll to make sure it'll behave properly.
To make the sushi rice properly sweet, add about 1/2 cup coconut milk and a drop of vanilla extract to approximately 2 cups of (cooked) sushi rice. This actually makes waaaaay more rice than you'll need, so feel free to reduce the amounts.
Add agave syrup to taste for a final dash of sweetness.