Paste will work, but you have to be in the right spot. Create a blank action in your destination project or single action list. Select that action by clicking on the little dot to the left of the completion checkbox. The entire line should be highlighted. Now paste and you'll get new rows for each line on the clipboard. If you paste while the action name is open for editing, you'll get a multi-line action name, instead of a bunch of actions.
Example list:
task 1
task 2
task 3
task 4
task 5
Project open, properly selected for pasting:
result after pasting:
The blank line is annoying, but more easily removed than typing in all those rows by hand.
project open, improperly selected for pasting:
result after pasting:
If you don't have that blank line in there and just have the project header selected, when you paste you'll get the lines on the clipboard turned into new projects, which seems like a bug to me, especially if you've clicked most recently in the outline, not the sidebar.