As I said, I don't know if iTunes stores gapless info as tags within the file or just within the iTunes database. You can see if tagging them in iTunes works by selecting all of the files within an album, edit the files (Get Info) and on the Options tab check "Gapless album".
Let us know if it works. If not, then I suspect the files will have to be edited with a third-part metadata file tagger.
Steve