One thing you can do is have the OK button disabled for 3 seconds.
Firefox does this when you install an extension.
Edit: All right, some people find this annoying. I still think that about 1 second would be all right. It would suppress the instant-OK-clicking instinct that people (myself included) have, and force a double-take. Of course, even this will annoy people if your dialog is not something that they actually need to read.
