Mix together the tequila, Cointreau, fresh lime juice, pineapple juice, water, and flaky sea salt until smooth and fully combined.
Fill each 3 oz Dixie cup, leaving about ¼ inch of space at the top.
Cut a small slit halfway through the center of each lime wheel and slide it onto a popsicle stick. Place the stick into the center of each cup so the lime wheel sits just on the surface of the mixture.
Freeze overnight, or until completely solid.
To serve, briefly run the outside of the Dixie cup under warm water for a few seconds, then gently peel away the paper cup.
Sprinkle with flaky sea salt or Tajín before serving, if desired.