If you consume all of either, by all means ask the sushi chef for more. People have asked if the ginger root in grocery stores is the same ginger that is pickled for sushi. It is, and up until now I have recommended that you buy it in jars at Asian markets. I recently found a recipe for making your own pickled ginger, and will share that with you. You can substitute a teaspoon of sugar for a Tablespoon of mirin , or an equal amount of sake .
Dry sherry is a potential but inferior substitute.
Scrub the ginger under running water as you would a potato for baking. Blanch in boiling water for one minute and drain. Combine mirin , sake , and sugar in a small pan. Bring to a boil, stirring until the sugar has dissolved. Place the ginger into a sterilized jar and pour the cooled vinegar over the ginger.