1. Add ginger to the bottled sake and refrigerate overnight.
2. Fill a martini shaker halfway with ice. Add 1 cup ginger-infused sake and shake until well chilled.
3. Strain sake into 4 martini glasses; stir in 3 tablespoons ginger ale per glass. Repeat to make 8 drinks.
4. Garnish each glass with a lemon twist and a strip of crystallized ginger on each rim.