Sure! Simple syrup is great because it's already dissolved and won't leave any sugar in the bottom of your glass, but it won't have the old-school vibe that a sugar cube does. If you can live without that, all you have to do is combine equal parts water and sugar in a saucepan. Bring to a rolling boil and cook until the sugar is dissolved and the mixture thickens a little. Let cool and store in a mason jar in the fridge.