This one is fun, I promise!
You’ll need some sodium bicarbonate (baking soda, NOT baking powder) and some very soft water.
Since making the video, I’ve thought more about this, and would recommend mixing a higher concentration of buffering solution.
Use 6.4g per litre of water. I would recommend starting by making 200g of water to 1.3g of sodium bicarbonate. On its own, this will not taste good. At all.
Keep this mixture in a dropper bottle like this one. If you’re shot is good, but just a touch sour, try adding a few drops of this. I would not recommend adding more than 2g per 20g of espresso. It’s not unsafe, it’s just not delicious.