1. Stop at a breakpoint.
2. In the "Stack" view, select some lines.
3. Right-click and select "Copy Selected Items to New Editor" from the context menu.

The editor which opens up then has some issues:

• Clicking into the editor below the last line causes the editor to scroll to its right end. This could be avoided if the editor's content had a newline at the end.
• The editor is in "unchanged" state but was not saved to a file. That means that the editor can be accidentally closed without any confirmation. As soon as I type a single character into the editor, it goes to "changed" state. That again means that whenever I trigger a build, Creator shows me a popup whether I want to save the editor. That can easily get annoying.
• "Diff Against Current File" from the side bar's context menu does not work with this editor.