A Lemon Drop is usually made with simple syrup, but Gaz Regan (author of our dog-eared copy of The Joy of Mixology) suggests swapping in triple sec instead. We dig it; it kind of tastes like a hard candy. Lemon syrup or oleo saccharum would bring an interesting flavor, too.
Traditionally, the recipe calls for lemon vodka, but you can substitute any citrus vodka (or rum) for an Orange Drop, Bergamot Drop, Yuzu Drop, etc.