Not only for MIHO, but everyone who wants to write Taiji a message - klick on the link in the blog - scroll down to 'Comments' with the number of already posted comments in brackets. (It's really tiny written)
Then when the site opened up scroll down until you see a form for writing the message
コメントを書く -- > Write a comment
お名前: --> Name
メールアドレス: --> E-mail
ホームページアドレス: --> Homepage
コメント: --> comment
To post the message click on the RIGHT button 「書き込む」
I don't know if it changed now but some time back it was necessary that at least one or two kanji were in the text included but you could have it a try anyway.
And as you said before, Taiji is not so good in speaking english, so make it a short message
But I really think he'd be happy to hear from his fans from overseas, as well
