To reduce spool-up time, both motors would need to be running all the time, with one slowed when the other increases its rpm.
It don't think the response would be faster than aerodynamically possible with ailerons in the main motor slipstream, as is currently the fashion.
A positionable jet outlet would be more practical, with the thrust generated on the centerline by a single motor exhausting into a bifurcated duct.. one feed to each tip, pointing aft nominally, and variable around a span wise axis to generate the roll moment.