XSL-FO: Column-specific markers

Would it be possible to have markers that appear at the top of each column in
a multi-column fo:region-body?

What I am hoping to do is something like a table of contents, split into
multiple columns. There would be several 'main' topics, with any number of
child topics below them. The topics would appear in alphabetical order, and
flow from one column to the next. Some of the main topics would have enough
children to take up more than one column. At the top of each column would be
the first main topic in that column, whether it was starting, or continued
from the last page/column.

I know this can be done by page, but I just need it to work by column as
well.

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