I asked Elliot and this was his response.
The flexible content field uses the acf_get_fields() function to load all children fields.
So, all you would need to do is make sure that the ‘sub field’ contains the correct ‘parent’ reference so that it is found by the flexible content field
Also, the sub field needs an extra setting called ‘parent_layout’ containing the string layout key.
Checkout the pro/fields/flexible-content.php load_field function
So, it should be possible. I don’t have time to test it out right now. I’ll do some testing to see if I can figure it out as soon as I can unless you say you’ve figured it out.
