Only by using extreme control inputs within a 4-6 second window could the situation be recovered.
But that is what you have to do in extreme situations, use the limits of the control available. 4 to 6 seconds is a lifetime in a critical situation.
All procedures for deployment of reverse in flight have the same starting point, thrust to idle, then shut down the offending engine, having confirmed it is the correct engine to shut down
Where asymmetric thrust is an immediate problem, get rid of the asymmetry.
I am not, for one moment, suggesting pilot error was the cause of the accident, but it was recoverable, and there was at least some advanced warning of a reverser problem.
At least some B767 simulators, at the time, had a model for reverse thrust in flight, but I have no idea of the parameters.
Tootle pip!!