I've heard about using glycerin in baking. I found this YouTube clip from Sweet wise
In the video description she gives amounts of glycerin
For every 500 grams, or roughly 1.1 pounds of flour or other dry ingredients, use 1 tsp glycerin.
For Fondant: Add 2-3tsp of Glycerin to 2 pounds of rolled fondant to help keep it smooth and avoid cracking.
Apparently the glycerin can help keep a scratch cake moist for...