i'll try to describe; i do this with my 8n / bush hog quite often.
tranny in neutral pto engaged clutch released. engage clutch and pto spins bringing mower up to speed. push in clutch and orc does its thing letting the hog freewheel. engage tranny in gear and let clutch out and start mowing.
maybe part of my situation is the design of the finish mower. no gearbox; the pto drives a large pulley which i would think adds to the inertia i need to dissipate when pressing hte clutch in. have lot more moving mass than just 3 mower blades. (woods rm306 mower)