Not the most elegant way, but you can "cheat" with MeshCAM by using smaller stock sizes with different offsets do do partial areas.
I'm not sure I've seen any CAM software that will let you assign different stepovers for different areas. At least not as one operation. Some higher end software will let cut the whole part with one tool, then, with a smaller tool, go back over just the areas that need more detail. Expect to pay several thousand dollars for features like this. I believe I saw it in an ArtCAM demo video.