I found out that there was essentially a duplicate question of mine, but specified in very different terms than the question I asked. Therefore, to aid future searchers or search engines, I don't want to delete the question -- people searching using the phrases I used should be able to find the duplicate question. But people shouldn't be allowed to post to my question either, because it is a duplicate.
However, there's no way to really tell the engine that the question should be closed as a dupe.
If the community thinks that the question is not a dupe, then one could use the same 5 vote reopen scheme used for current closures.
(For the record, I saw this question which is similar, but what I'm looking for is more specific in that I think the only valid closure reason should be duplication)