I'm just a hobbiest, so I make cakes infrequently. The sleeve fillings are pretty big and I usually have a bunch left over after making a cake. If you have come up with some interesting ideas to use the leftovers, please post. Here's mine.
Simple Rugelach. Just take some crescent dough, roll it out fairly thin, cut into small triangles. Spread the filling on, roll up starting from the wide end. Brush with beaten egg, sprinkle sanding sugar, bake at 375 deg. until quite brown. You could also top with ground almonds, or add to the filling.
If you don't want to use store-bought crescent dough, you can make your own rugelach dough. Here's a link to a recipe. http://allrecipes.com/Recipe/Rugelach-2/Detail.aspx
My daughter had so much fun making these to bring to her dad at work last week. She had even more fun eating them!
I am new to cake decorating and just a hobbiest also. You can also use the sleeve filling for filling cupcakes.
I recently had some lemon leftover and I froze it for a use later on! Not really creative but it would help you from having to keep buying it over and over and not being able to use it all.