I removed the remaning wing frame from the jig, removing the skins that were clecoed to it, and putting it to the side. Doing so allowed me to use the centre part of the jig to rivet the leading edges.
As per the instructions, I riveted toward the the front of the leading edge. I did this one rivet at time, removing the clecos, which were in each hole. one at a time. I wanted to avoid any 'smiles'. which, I'm happy to say I actually managed. There were a couple a small 'smiles', but I found that if I held the rivet gun straight onto the rivet and gave the trigger a very quick, short squeeze the 'smile' disappeared, and the surface was nice and flat.