I didn't get any answers, so I guess there is not an easy solution to this problem.
Tell me what you think of this workaround:

1 instead of starting sub-entries on a separate line, type a * and then write in the subentry on the same line

2 finish list, and sort it

3 search and replace * with ENTER + TAB

will this work?

in search and replace, what are the proper names for ENTER and TAB, and where do I find them?