Basically I have segmented the file in question into much smaller files. I then decrypt a smaller segment file when needed for use and re-encrypt it when no longer needed. While this approach may not work for anyone else it is a strategy that fits well with how data in my application is used. I have found the decryption/encryption process surprisingly quick. It is true that a file is in an unencrypted state while in use - I am willing to live with that risk.