To turn the bur on a curved scraper, I often use a nail set while clamping the scraper in the vise. The set isn’t the ideal, polished metal you’d wish for, but it helps me for two reasons. First, it is tapered. This means I can bear straight down yet still be applying pressure at an angle to the edge. This makes it easier for me to follow the curve. Second, the diameter is quite small, which means less force is required to generate adequate pressure. There must be better ways, but this is somewhere between passable and good.