[gcrump]

Not sure how close this script will get you but I use it to do much the same thing. The first line is the primary topic and then all other lines are sub topics. I use this when I want to flesh out a subject on the fly. You would have to enhance it to deal with multi-headings.

tell front document of application "OmniOutliner Professional"
set passcount to 1
repeat with currentLine in every paragraph of (the clipboard as string)
--- on first pass make the first line the project starter
if passcount = 1 then
set passcount to 2
set theProject to currentLine
display dialog "About to add project..." buttons {"Cancel", "Add"} default button 2 default answer theProject with title "Project from Clipboard"
if button returned of result is "Add" then
set parentRow to make new row at beginning of rows of (first child whose topic is "Inbox") with properties {topic:theProject}

else
exit repeat
end if
else
make new row at end of parentRow with properties {topic:currentLine}

end if
end repeat
end tell