Yeast won't hurt you, it's in beer!
Yeast doesn't grow well in high sugar concentrations (sugar in large amounts acts as a preservative). If the yeast is supposed to be alive and vigorous, I wouldn't use more than about a teaspoon of sugar to a cup of water. Pure sugar is also a poor diet for yeast (only junkfood), you could throw in a pinch of oatmeal and that will balance out their diet with nutrients.
You could try the same thing with a dab of yogurt or sour cream, those contain lactobaccillis which will also eat the sugar and might smell like yummy decomposing stuff to slugs and snails.