How to thicken icing without powdered sugar?!
Two good ways to thicken without sugar.
Beat room temperature Cream Cheese, until it's light, then add your icing a little at a time, until it's incorporated fully into the cream cheese. This will make for a heavier icing.
Beat heavy whipping cream, without sugar, just a little vanilla extract. When the cream is whipped, fold it into your coffee icing 1/3 at a time. This will make a lighter icing.
You mentioned that the icing is way sweet now. After you use either of these methods, it won't be as sweet, and you can adjust it with a little honey, or light corn syrup.
do you happen to have a brick of cream cheese? soften it and blend a little of your icing at a time into the cream cheese.
You could also start a white sauce, 2 tablespoons flour and 2 of butter. blend well and stir the icing into it in a sauce pan. Heat on medium low and keep stirring until it gets thick. and it will!!
Stir one tbsp cornstarch into a bit of cold water. Stir into your icing. Heat in microwave for 30 seconds at a time, stirring well between heating. After 1-1/2-2 minutes, allow to cool. This should thicken the icing up.
If you ran out of powdered sugar, you could also grind some powdered sugar in the food processor.
Im a baker myself, you can add light corn syrup to it... but not too much. Hope this works.
if it is to sweet add 1/4 teaspoon of salt