Widgeon - that's the stuff of nightmares.
We used to operate BO105's, and I seem to remember we had one which had two degrees of negative pitch. It's a long time ago, and I've a memory like a whatsit, but there were certainly no special procedures for applying negative pitch.
My own experience of negative g, again in a BO105, was while enjoying a flight over the Western Isles. I flew into a terrific downdraught, and became aware of a sudden vast increase in pressure on the shoulder harness, my feet flying off the pedals, clouds of dust rising from the floor, oil pressure warning lights coming on, with the pressures indicating zero, and all the while the passenger pushing up on the cockpit roof as hard as he could, barely managing to suppress a scream.
It probably didn't last more than a second or so, but I'm sure it shortened my life by a few years. My thought at the time was, "Of all the helicopter types in the world, thank God I'm in a Boelkow."