Some misunderstandings here.
1. There is no need to "gently push up" once inverted to get -1G. You are already there just by being inverted.
2. As stated, the nature of the problem required zero G, not negative G. -1G would be just as bad under those circumstances as +1G.
0G can only be achieved in a ballistic path (or at a legrange point, but that would be very tricky to achieve under these circumstances!)
3. "I haven't flown fast jets and not done that much aerobatics, but could they not have climbed up into the 10s of thousands, above the cloud (or even in the cloud with radar separation) before attempting a level outside turn pushing constant -ve G around the turn until it's up and locked?"
Their idea was misguided.
Yours is insane, and shows a little lack of understanding of G.
Why turn? What is the added benefit?