Wouldn't you be better soaking the raisins and then threading them along a horses tail hair and then snipping between the raisins so that a little bit of hair sticks out either side. Pheasant then comes along and pecks it and the raisin gets stuck in its throat and pheasant will then stand still. You then just go along and neck it. Simples.
Pheasants sleep on their roost without falling off so not totally sure that the sleeping tablet thing really would work.
In the book, the chap should have necked them as he collected them. Rookie mistake IMO.