KOMA: Margin notes only on outer side of two-column document? [closed]

Question

For some part of a two-column scrbook of mine, I need to actually get a three-column layout: Two columns text, and a third column with a table (or a boxed enumeration, that would work too).

Both columns of text and the table / enumeration have to be shorter than a page (for contextual reasons), so column / page breaks are not an issue here.

I was hoping to somehow commandeer geometry and \marginpar (or similar) for the purpose - setting a 1/3rd textwidth margin with \newgeometry, and then pushing my "third column" there.

However, setting up margins for a twocolumn document gives a margin on both sides of the page.

\documentclass[twocolumn]{scrbook}
\usepackage[german]{babel}
\usepackage[utf8]{inputenc}
\usepackage[marginparwidth=2cm]{geometry}
\usepackage{lipsum}
\begin{document}
\marginpar{Hello.}
\lipsum[1-4]
\marginpar{You.}
\end{document}

Now, I could tweak the page geometry a bit so that the inner margin gets pushed off-page, and set the \marginpar (or whatever) in the second column on recto pages and in the first column on verso pages...

But before I do that hack-ish thing: Is there, by any chance, a switch in either KOMA or geometry that would tell LaTeX that I want only one margin on the outer side of the page, with \marginpar's from the inner column being pushed there too?

Edit: Or generally a better way to achieve a "temporary third column"?

Edit 2: Apparently, no "easy" way to get margin paragraphs "moved over". On second thought, it wouldn't make much sense, from a typographical point of view, since it wouldn't be clear which column is annotated. Ah well, I'll hack my way around it. ;-)

Voting to close as "too localized" myself.

Answer 1

Add the option \documentclass[mpinclude=true]{scrreprt}, which expands the margin space, so \marginpar{...} perhaps can be used the way you want.