Create a water + baking soda solution?
Baking soda is soluble in water at up to 90 grams per liter. If you add more than that to water, you'll end up with a saturated solution at 90 g/L plus some crystalline baking soda on the bottom of the container.

A teaspoon of baking soda has a mass of about 4.8 grams, so it'll take 53 ml of your saturated soda solution to deliver 1 teaspoon baking soda. In Fully metric terms, that's 11.1 ml of solution per gram baking soda.