Ansible nested variable in playbook

I'm trying to use getent to lookup a user's home directory and then apply that information to a copy job. I know we can't do nested variables, but I'm just stuck. I have been playing with the lookup('var's...) syntax and various ways to pull a value out of a dict. In this particular case I do know the user's home directory, but now it's more an exercise in figuring this out. ANSIBLE_USER is defined as ansible

My playbook is:

#lookup ansible user's home directory
#drops the value into a getent_passwd variable
- hosts: all
  become_user: root
  become: true
  tasks:
    - name: get info
      getent:
        key: "{{ ANSIBLE_USER }}"
        database: passwd
    - debug:
        var: getent_passwd.{{ ANSIBLE_USER }}.4
    - set_fact:
        ANSIBLE_HOME: "{{ getent_passwd['ansible'][4] }}"

- hosts: all
  become_user: root
  become: true
  tasks:
    - name: copy iptables files
      copy:
        src: "iptables/{{ IPTABLESCONFSRC }}/iptables.sh"
        dest: "{{ ANSIBLE_HOME }}/temp/iptables.sh"

This works because I'm manually defining the 'ansible' string in the ANSIBLE_HOME line. However, what I'm functionally trying to accomplish is:

ANSIBLE_HOME: "{{ getent_passwd['{{ ANSIBLE_HOME }}'][4] }}"

The best I can get is a undefined variable error because I end up looking for: getent_passwd[ansible][4] or getent_passwd.ansible.4 and that doesn't exist via:

ANSIBLE_HOME: "{{ lookup('vars', 'getent_passwd.' + ANSIBLE_USER + '.4') }}"

or

ANSIBLE_HOME: "{{ lookup('vars', 'getent_passwd[' + ANSIBLE_USER + '][4]') }}"

The debug output shows:

ok: [HOSTNAME] => {
"getent_passwd.ansible.4": "/home/ansible"
}

This seems to work because the debug var is already considered Jinja, so it's effectively double nesting for you.