It would be difficult to see how they'd implement that in the "Voltec" system.
The drivetrain is fairly complex, it's a "series" hybrid, instead of a "parallel" hybrid like the Prius. There's a planetary gear which operates in reverse to how the Prius drivetrain operates; in the Prius the engine is connected to the planet carriers, the secondary motor/generators are are connected to the sun gear, and IIRC the wheel output is taken from the ring gear. The ICE is directly connected to the drivetrain at all times.
In the Volt, the main electric motor is connected to the sun gear, and the wheel output is taken through a reduction from the planet carriers. There's a secondary electric motor/generator with a clutch to both the ICE and the ring gear, which is used for regenerative braking, and when running on gas operates as a generator for the main electric motor.
But since there's a clutch on each side of the secondary motor/generator, at "high speeds" (some have said 70 mph, but AFAIK there's no hard cutoff, it's whenever the computer decides it would be most efficient to do this) the car can engage both clutches, so the gas engine can turn the ring gear directly, along with the main motor.
Diagram:
The Gen 2 Volt, which was released for 2016, is more complicated and has about 6 different operating modes..I don't fully understand it yet...