Access delegated hosts variable while include role - ansible

Question

I've an inventory as follow:
[central]
central_1
central_2
[peripheral]
peripheral_1
peripheral_2
...
central_1 and central_2 share the same database and each peripheral_* has its own local database.
Connection parameters are all stored in group_vars/central.yml and multiple host_vars/peripheral_* files.
Then I have a bunch of roles that access the database and perform specific operation based on values in peripheral_conf hostvars.
My goal here is to run a subset of the roles on one central host using the right DB access parameter.
First attempt
First attempt was to have two different play in the playbook targeting different hosts
- hosts: peripheral
pre_tasks:
- name: Load Configuration
set_fact:
peripheral_conf: "{{ hostvars[inventory_hostname] }}"
roles:
- role1
- role2
- role3
- hosts: central
roles:
- role1
- role2
but, since I normally run the playbook limiting the inventory to a specific peripheral host, I'm not able to run it against the central hosts.
Second attempt
I then tried to include role using delegate_to and delegate_fact:
- hosts: peripheral
gather_facts: False
pre_tasks:
- name: Load Configuration
set_fact:
peripheral_conf: "{{ hostvars[inventory_hostname] }}"
tasks:
- name: Insert values into central DB based on peripheral configuration
include_role:
name: '{{ item }}'
apply:
delegate_to: central
delegate_facts: yes
run_once: yes
loop:
- role1
- role2
roles:
# insert values into peripheral DB
- role1
- role2
- role3
but it keeps using peripheral's DB connection parameters.
Working attempt
I finally was able to make it works adding an explicit overriding of the connection parameters:
- hosts: peripheral
gather_facts: False
pre_tasks:
- name: Load Configuration
set_fact:
peripheral_conf: "{{ hostvars[inventory_hostname] }}"
tasks:
- name: Insert values into central DB based on peripheral configuration
include_role:
name: '{{ item }}'
apply:
delegate_to: central
run_once: yes
vars:
db_host : "{{ hostvars['central_app1']['db_host'] }}"
db_database: "{{ hostvars['central_app1']['db_database'] }}"
db_username: "{{ hostvars['central_app1']['db_username'] }}"
db_password: "{{ hostvars['central_app1']['db_password'] }}"
loop:
- role1
- role2
roles:
# insert values into peripheral DB
- role1
- role2
- role3
And finally, the question
The playbook does the job but I'd like to know if this is the only way of do this or there is any better and/or more efficient way to do this.