I've never heard that it was necessary for a man to eat the afterbirth to enable him to lactate...

All it takes, or so I have always been told, is an actual desire to feed a baby, and constant practice
Lactation is very much a supply and demand operation. In a mother, the process begins with certain birth related  hormones, certainly, but if no child suckles, milk production ceases quite quickly. When the infant drinks more, the milk ducts produce more, and visa versa.

All a father (or other interested man) needs to produce milk is the want, and the opportunity. If the baby is getting enough food to avoid dying for the week or so it takes for lactation to begin, he can feed it entirely satisfactorily from there on, and experience all the fun of breast feeding :)