What if you put a liner of foil in the mint tin first. Make the foil liner oversized so that it stands up higher than the sides of the tin. Melt you wax and pour into the tin. When it cools, you could fold the foil down over the candle makeing an additional layer to keep the wax from spilling out. Then close the lid of the tin.

If you don't need the windscreen, fold down outside the tin to help prevent wax spills.