Pour the lemonade into a small saucepan. Add the sugar if using (depending on how sweet the lemonade is, you can choose to add sugar to make the shots sweeter). Sprinkle with the gelatin and allow it to soak for a minute or two. Heat over medium heat, stirring constantly, until the sugar and gelatin have completely dissolved.
Combine the lemonade mixture with the beer and vodka in a large liquid measuring cup with a pouring spout.
Put 16 clear plastic 1-ounce shot glasses on a baking sheet. Pour the lemonade mixture into the glasses, filling them about three-quarters full. (You should have 1/2 to 3/4 cup liquid remaining in the measuring cup.) Refrigerate the shots until just lightly set, 30 to 60 minutes. Leave the remaining lemonade mixture out at room temperature.
To create the foam: Add 1 tablespoon of the coconut cream to the remaining lemonade mixture. With the whisk attachment on an immersion blender or hand mixer, whisk the mixture until foamy. Spoon into the tops of the lightly set shots and refrigerate another 2 to 3 hours. If the foam starts to get thin, add another tablespoon of the coconut cream to the remaining lemonade mixture and repeat the process.
For an extra fun step, buy a full sheet cake covered in green frosting and add the jelly shots to emulate a beer pong set up.