Scoping in data_template's

Configuration
1

Is there a way to use the values of one data_template’s variables in another template within the same entity?

Here’s an example (that doesn’t work):
(a script)

random_test:
  alias: Random Test
  sequence:
    - service: persistent_notification.create
      data_template: 
        message: >
          {%  set items =      
            {
            "title one":"value 1",
            "title two":"value 2",
            "title three":"value 3",
            "title four":"value 4",
            } 
           %}
           {% set index = items | list | random %}
           The value is {{items[index]}}
        title: The title is {{index}}

In this example, the message correctly gets a random element from “items”. But I’d like to use the index in the title for the persistent note.

Is there a way, within templates, for me to make that kind of scope work?