That does seem like a cool method!
Unfortunately, Symantec offer no similar option for OS upgrades on an SEE-FD Encrypted disk (AFAIK). Usually, the reason for doing an upgrade is to maintain user files and the like, in which case you may want to look into using the SEE Access CD to gain access to the encrypted disk(s), copying required data out, before then doing a full re-image (with Win7) and installing/encrypting again.