Redirecting old permalinks in bulk

So I did a bad thing a while ago and didn’t notice until now. Some time ago I apparently changed the permalink structure (I think it might have been when we moved from WordPress-hosted to our own servers but I’m not sure).
Now I have a 404 monitor (which I should’ve gotten ages ago) and it gets thousands upon thousands of hits for old permalinks (domain.com/day/month/year/post when the new is domain.com/post).

I know you can get tons of plugins to handle 301’s, but all I’ve found requires you to put in the url’s manually for both the old and new. Since the structure should be regex-able (is that a word?), you should be able to do it automatically, right? Except I don’t know nearly enough about fiddling with server files to know even where to start looking to make such a script.

Could anyone help me out? Because we’re talking about 1500+ url’s here and I really can’t go over them all manually.

The page I need help with: [log in to see the link]