I don't think you can. Much like form features, they are not calculated because there is no bend involved.
However, I have worked with flattening a quilt to get a very good pattern for such features.
This would not be done in sheetmetal.
This is a part that is curved in two directions. This also does not flatten in sheetmetal. Some careful consideration for where to place the quilt and I am certain this is a very close flat pattern of the part (the blue colored surface).
