iTunes duplicate song syncing question

If I had unprotected AAC songs that I wanted to convert to MP3 for playback on a phone, what's the best way to do this in iTunes to ensure that the iPod doesn't sync both the AAC and MP3 versions?

The only way I see to do this is to simply uncheck the dupe MP3s and tell iTunes to only sync checked songs. But with potentially hundreds of check marks to undo, there simply has to be an easier way...right?