How do I get duplicates off of my iPod...even though there are none in my library?

I got a new computer recently, but because I didn't have all my music files on my new computer, I downloaded my iTunes purchases from the cloud. However, not all of the songs on my iPod were bought from iTunes, and I stupidly deleted the files from my flash drive permanently, so for now I've been manually syncing my device so that I can simply add on songs when I need to. Nevertheless, all of my most recent purchases have at least one duplicate of themselves on my iPod...but this doesn't show in the iTunes library because I haven't synced the device yet (nor do I want to as it would delete all the tunes that aren't yet in the library). How can I delete these duplicates?