However, everything people have suggested should give the practical results you want, even if it's not what you asked for. Do you have a large amount of unstockpiled obsidian elsewhere in your fortress? If so, why have you set up an obsidian farm? Stockpile that shit and use it.
That's a fair point. But the situation was that I had some obsidian areas, but it turned out that this was limited to the upper levels that I'd set up living and work spaces in, so short of strip-mining that and rebuilding, I had a rather limited supply. I didn't want to run out of valuable craft and furniture material, but at the same time there were still enough loose obsidian rocks scattered around to confuse the haulers about what I was trying to accomplish.
As far as the actual obsidian farm, the no-input stockpile is actually a good solution. Where it gets annoying is say I'm mining later and carve out a small area of realgar. Ooo shiny, I'd like carry some of that back to the main fortress area for color-coded levers and whatnot. But again there might be a few random chunks scattered around in other places that I don't really want to haulers to bother with. Since their idea of "closest" is as-the-mole-digs they can waste an awful lot of time going after random rocks. Setting up linked stockpiles every time seems like a pain, but I guess that's what I'll have to do.
Maybe I'm just expecting an unrealistic level of efficiency from my
lemmings dwarves.