Place sugar and water in medium saucepan over medium heat. Bring to a boil, using a wooden spoon to stir occasionally until the sugar is completely dissolved, about 2 minutes. Remove from heat and let cool 5 minutes.
Make simple syrup into flavored syrup:
Place the ginger, lemon, and the simple syrup in a blender jar, cover the jar, and blend on lowest speed until the solid ingredients are roughly chopped, about 1 minute.
Turn off the blender and let the mixture steep for 10 minutes. Repeat, this time blending the syrup on medium speed for 1 minute, then shut it off and let steep 10 minutes more.
Strain the syrup through a fine-mesh sieve lined with 2 layers of water-moistened cheesecloth over a medium bowl. Store syrup tightly covered in the refrigerator up to a week.
To serve, fill a glass with crushed ice and 3/4 cup seltzer. Top with 1/4 cup ginger-lemon syrup and stir. Adjust flavor with more syrup or seltzer as needed. Garnish with a lemon wheel.