While happily making progress on what will (I hope) become my cousin's new favorite purse, I realized that I was way past the point at which I had planned to do some increasing. Since I'm designing this as I go along, I could have just kept going, but I really have my mind set on a certain style. Of course I could have frogged, it is just knitting afterall. But frogging is no fun. Besides, I have gained some insight from all this sock and lace knitting - it is possible -- and not all that difficult -- to make an increase several rows, even a dozen or more, back. If you've ever dropped and then recovered a stitch, you've already almost done it. Curious? Here's how:
Notice that there are ladders inbetween the stitches. You follow the ladder down to where you want to add an increase. Take a crochet hook and lift the rung of the ladder where the increase should be. This will become the new stitch. Take a crochet hook and pull it out a little to create a loop. You could treat this as a dropped stitch and just follow the ladder back up to the top, but that will create a hole. To close up the hole, you have to twist the loop before pulling the next "rung" of the ladder through it. The other stitches should not be twisted in the same way.
This worked well on stockingnette stitch. It would be trickier on garter because you would have to change the direction in which you pull the "rung" through the loop - but it's still no different than bringing home a runaway stitch.
Because this is a felted project with only a few widely spaced increases, I wasn't worried about whether I did a left-leaning or right-leaning increase. It would take a mind much more clever than mine to get down to that level of detail.