Looking for help with a Multi-Network Multi-Site Configuration (I'm almost home!)

I'm Almost Home and Need Someone With Extensive Knowledge on Networks for WordPress
Hey Support! I hope you're all having a great day/morning/night? :slight_smile:

Before I start, I know this is complicated and few have reached the top of this mountain but I believe I'm almost there and just need a little help. I know this is possible to resolve, I just haven't figured it out where to put the code yet...

Scenario (In Play) -
FYI "Support Access To My Site is Turned On"

Standard WP Multisite Setup
Networks for Multisite Configured
BuddyPress Multi-Network Installed (BuddyDev)
define ('BP_Enable_Multiblog', true);
Domain Mapping Setup

Everything is working SWEET! (except one thing)

I added (second 'Network') secondcoolsite.com ---
Then created sub.secondcoolsite.com
Mapped sub.secondcoolsite.com to (mynewsite.com)

Here's where I'm stuck...
When someone joins (mynewsite.com) and want's to setup a subdomain It can't resolve back down to (secondcoolsite.com) It needs to resolve to (mynewsite.com)
e.g. lookat.mynewsite.com --
not lookat.secondcoolsite.com --

There has to be a simple solution to this that can either be solved through the database, .htaccess, functions.php, or wp-config.php

Your help/thoughts would be appreciated!!