I am going to have some hints for you. In the past, I have typeset vertical text by other methods than multicol…
Looking back through documents, I have things like this:
In isolation this code does not mean much, it is just a way I found to rotate a single little page with a line of kanji.
Also, you need clever ways to rotate the character “–”, (ichi) which appears quite frequently. I seem to recall some documentation for xeCJK that is in Chinese, but can be deciphered with effort.
Also, there are a few other \LaTeX heads here.
Here is a workaround in isolation:
I used this to rotate ichis. Where there is an ichi in your doc, you just use the command \stick. I don’t know how I came up with the 0.75em hspace. Maybe I should document better!