Alternatively, is there a way to separate out the few hens who are not faring well? Sometimes a rooster has his favorites -- either the hens are "easier" to mate, or have some other attractive quality about them. Also some hens have more brittle feathers and tend to suffer more feather loss from a rooster's attentions.
The other thing some people do (I haven't tried it), it putting chicken saddles --basically little cloth aprons that protect their backs -- on the affected hens. I prefer to separate if it is at all possible. If you can't and you don't want to do saddles, the hens will probably survive, as long as they have shade in the daytime, and are not bleeding from the excess attentions.