Is there a plugin available to automatically combine duplicate contacts? Instead of the manual process required by Locate Duplicate Contacts?

We have a very large contact database (~20,000) that we very recently migrated over from Now Contact. We had to import some of the Now Contact via a text file, but because many of our contacts did not have email addresses, the important was unable to see them as unique and created brand new entries.

Now we've got thousands of duplicates. Has anyone written plugin that might allow us to combine these in a single automated (or semi-automated) process?

If no such plugin exists, would it at least be possible to build something like this using the SDK? I've got a pretty decent grasp on Cocoa development, and the SDK documentation I've read so far seems straightforward (although I wish there was more of it).

Thanks.