[viddy]

You could try Soundtrack Pro. I haven't really used it at all, but I'd imagine it would have a limiter plugin in it.

The kind of limiting you're talking about doing, is just lowering the limiter's threshold to something like -0.5db or even -0.2db, that way it will only activate at the very peaks of the sound. Just make sure the attack and the release is very short (if there are settings for this in your plugin).