With the passenger's side cut out, the next step is to fold the cut out portion of the new insert onto the uncut driver's side. Flip the insert over, scrim side up, and fold the cut portion of the insert onto the uncut end, folding along the centerline, again lining the pleats up along both edges of the insert. Put the weights on the insert to hold it down as you go along. It takes a bit of playing with to get everything lined up, and applying a weight here and there as you get something just right sure helps. We're not trying to stretch any of the fabrics - we're just trying to manipulate them into place. You'll have to go back and recheck things before you start tracing, and you'll most likely have to readjust things a bit here and there, but this is no time to cut corners - not unless you like crooked pleats and such.
With everything lined up as perfectly as possible, and everything weighted down, I traced the outline of the cut out portion of my insert onto the uncut portion with a Sharpie. The next step is to cut out the rest of the insert, again cutting along the inside of the line.
Picture 1: The cut out portion of the insert is folded over onto the uncut portion, and weighted down to hold everything in place. These weights weigh around 5-lbs. apiece.
Picture 2: You can see where I've traced onto the scrim with a Sharpie pen. Also notice that my pleats are lined up as perfectly as I can get them without stretching anything.
Picture 3: After removing the weights and unfolding the insert, it's just a simple matter of again cutting on the inside of the line. The seat back insert is now cut to final shape and size. The contrast between the white scrim and black thread sure shows off how wobbly I got when sewing the pleats into the insert. Good thing it doesn't look this bad from the outsideâ€¦