I don't know that I would attempt without a serger either. Those jersey knit's have a tendency to stretch all over the place. Other than that, when I have large amounts to cut from hems...I measure x from the bottom of the hem edge once it's turned under. Leave usually about 1/4" to turn under at the cut edge to make a nice clean edge on the inside. You could attempt this with the 'blind hem' stitch on your regular machine if it has one. If you've not used that feature before, read the directions about 6 times before you attempt on your final product. The piece of fabric usually needs to be folded all kinds of goofy ways to get everything to work correctly. Not sure if you can do that with a walking foot which would probably help with the stretch.
Good luck!