Nevermind, it did work.

src/compare/diff.rs

@@ -331,6 +331,17 @@ pub(crate) fn artificial_diff_scope<'b, 's>(
     .into())
 }
 
+pub(crate) fn artificial_owned_diff_scope<'b, 's, 'x>(
+    name: &'x str,
+    children: Vec<DiffEntry<'b, 's>>,
+) -> Result<DiffEntry<'b, 's>, Box<dyn std::error::Error>> {
+    Ok(DiffLayer {
+        name: name.to_string().into(),
+        children,
+    }
+    .into())
+}
+
 pub(crate) fn compare_ast_node<'b, 's>(
     source: &'s str,
     emacs: &'b Token<'s>,