There's no way to do it with the built-in delimiter options, but you can do it with minimal scripting.

Add a Script activity above the one that sets the field values (SDK Script works too, but we don't need the Laserfiche connection overhead on this one), set it to use C# and open the script editor. Under "//Write your code here" add the following:

  string delimiter = Environment.NewLine + Environment.NewLine;
  SetTokenValue("delimiter",delimiter);

Close the script editor. In the token editor you're showing above, change the indexing option to "the value at index" and from the token list next to it, choose the script activity and then the "delimiter" token it creates.

Save and publish your workflow. At run time, the workflow will log a warning about the delimiter token not being a number, but actually work as you wanted it.