we had a few trees taken down about 6 years ago, those stumps where bulbs or short planting were about it I piled some soil on top of the stump and let mother nature work on it. two of those stumps developed a soft center, so I shoveled out the soft wood, and put soil in it, then planted a few of my extra hardy geraniums which now are cascading over the edge. I have also places a flat pave stone on the edge and put a decorative garden statue on it. But---in the long run will leave them to rot out naturally. However, -----there was another stump that had nothing growing around it, so I kept piling dry twigs, limbs, ect. and used it as a burn spot, after only perhaps 3 years of burning on top of that stump it finally went to level. So took our heavy truck and ran over it flatting it out more. Today you can hardly see where it was, grass is growing nicely over that area.
but of course you could call a company who does stump drilling, I heard the cost is pretty high.