That doesn’t really make sense. For a velocity system, D would be driving the acceleration to zero. The applied voltage is directly proportional to the acceleration of the wheel, so zeroing the voltage immediately halts acceleration; this is different from how position systems work. Therefore, you don’t need D: just a better tuned P.
Flywheels are single-pole systems, so the P gain can move that pole wherever you want (I won’t go into what poles are). That is, the exponential decay response can be as fast or as slow as you want without oscillation, assuming you sample fast enough to keep up with the flywheel system dynamics.