I was reading on RaidenFTPds forum about this and I saw FlashFXP wasn't listed. Thought I would just bring it to your attention so you could begin working on this.
http://www.raidenftpd.com/en/features.html
note : MODE Z implementation is based on IETF draft, and is not a proprietary protocol of RaidenFTPD, the original authors of the draft are J. Preston (NSC) and TJ Saunders
-guru