How do you topstitch a small curve? The same way you topstitch a straight line, only you follow the curve. I aim the middle of the left side of my welt foot on the seam to get a stitch line slightly less than 1/4" away from the seam. If you have to use the hand wheel on the sewing machine and do one stitch at a time, as long as it gets done right it doesn't matter how you do it. The only way you can get in trouble is on a sharp 90 degree turn, those are hard to do and get them to look good.
No one lives forever, the trick is creating something that will.