If there is currently some way to distinguish a jpeg created by software in a camera from a jpeg created by editing software, I'd like to know what it is. If there is, it is nothing software can't fix to make it indistinguishable.
And if there is, the most obvious hack (keeping pixel size in mind) is to edit the RAW file to kingdom come, print it out, take a photo of the print and let the camera make a jpeg.