Fuji:
Hopefully they've got their act together since last October when I telephoned the FAA Head Office in Oklahoma City about the 'piggy-back' issue.
At that time they hadn't got the faintest clue: they insisted that it all had to be done in person at a nominated FSDO and deffo could not be done by post.
If you have anything in writing like an official declaration on a FAA website I'd be grateful for a link, as I can't find any official/written conformation anywhere.
Cheers
Cusco