Adding quilt top to pre-sewn duvet cover?

I saw someone post about a quilted duvet cover the other day, and I absolutely loved it! The thing is, I have the duvet covers I need for the foreseeable future. I can't justify making another set. But, has anyone tried making a pieced top and quilting it to just one layer of a pre-sewn duvet cover? If so, how do you do the edges? And I'm guessing there is no need for another layer, especially if the duvet cover is flannel?