Sandpaper is fast and harsh (although at first you might be surprised how well the leather is taking it). Start with a fine sandpaper and work your way up to coarser papers. The sandpaper will scratch up your leather and is best on edges and seams (especially if acetone doesn’t help). Sandpaper is not recommended before alcohol or acetone application. As a matter of fact, you may want to rub in some conditioner to keep your garment from drying out and cracking from the damage.
Rub the garment aggressively into pavement, such as a sidewalk.
Put your garment in a cement mixer with some gravel and turn. Or you can try putting some gravel into a 5-gallon bucket and sealing your garment inside, and then putting the bucket into your trunk or the bed of your truck during a drive, so that the bucket rolls as much as possible. Or you can tie the garment to the back of your vehicle and drive through a gravel lot, or down a gravel road.