This is such a great idea and something I am going to try the next time I am frosting cupcakes! I use a frosting bag with tip and those bags are such a pain to come clean...but here is a trick to eliminate that!
Wrap your icing SARAN WRAP
then insert that into the piping bag...pull the saran through, and cut the top off.
Then attach your tip like normal
When you are done, just remove the saran wrap icing and your frosting bag will be clean!
There are more detailed instructions HERE! Go check it out!!!!
photos found at The Farm Girl Recipes