You mentioned real frosting.  The only one I have ever seen that isn't all fat and sugar, is one from Kathy Hoshijo.  Alas, it is not vegan, but I think it could be.  She used honey iwth noninstant, nonfat milk powder.  (the NONinstant nonfat milk powder is the consistency of powdered sugar and doesn't have the burnt taste that instant does.  Instant did not work for that recipe.)

I don't usually keep soymilk powder, but I know you can get it.  Perhaps you could experiment with a smaller amount of EB and a liquid sweet like rice syrup with soymilk powder for a great deal of the powdered sugar.  It would not be perfect, but if it worked, it might be nice with less fat and less sugar. 

Come to think of it, I believe I have a small quantity of vanilla flavored soymilk powder from Dixie Diner that would be good for this because it is not that nice to mix and drink.  I'll keep you posted.