Filter based on item URL

I have a strange problem with one of the feeds I am currently importing. I am getting a ton of duplicate items because the feed is creating different URLs for the same items. And that defeats the duplicate filter of Feed API.

All items come through with this string on the end: /-1/rss

But some come in with /-1/rss01, others with /-1/rss02, etc.

What I would like to do is find a way to strip out this part of the URL when the items are loaded, so I don't get duplicates. Is that possible with this module?

Thanks.