I envision a new temporary HUD element consisting of a large opaque circle that appears over the crosshairs and exterior action whenever your Mech is in danger of losing its balance due to collision, falling or other extreme event. Within the 'A' circle, a much smaller 'B' circle outline would be centered. Finally, a 'C' circle or pip would appear at a distance from the center of B representative of the severity of the Mech's imbalance.
So, for example, a Jenner running at 130kph into a stationary Atlas would have a "balance overlay" pop up over their crosshairs, with the C pip at the bottom of the A circle, like so:

The C pip appears at the bottom to reflect the force acting on the Jenner to fall over backward. A less violent collision would have the C pip closer to the B circle.
The WASD controls now control the movement of the C pip for the duration of the imbalance as the player tries to center the C pip for the next second or so. If he succeeds, the Mech recovers its balance; if not, it falls. Once the outcome is determined, the overlay disappears and controls are restored.
The size of the B circle and the speed of the C pip could be influenced by Mech type (some designs more stable), piloting tree unlocks, and even modules.
The entire overlay could even be disabled in game options by default to avoid newbie overload.