How to bulk add aliases from a cck field?

A little background: our site was Wordpress & vBulletin and some glue to make Wordpress articles link to forum threads.
We've moved to Drupal and managed to migrate in all the Wordpress articles, but didn't manage to get the old urls to migrate in.
However, I created a cck field and stored the old url for each imported article in that cck field.

Here's the question: how can I take the value in the cck field of each of these articles and (after some cleanup), add them to each imported node as an additional alias?

I could attempt to set up pathauto to use the url pattern of the old articles, but I'm not entirely sure I've got that pattern right. So I'd prefer to add the actual old urls.
(By the way, the reason I want the old urls working is that the vBulletin forum archive still contains links to them).

So what's the best way to do this? Would there be a mysql method maybe? I'm not averse to doing something with queries if I can figure out what query to use (I don't really "know" mysql).