Like the others have said, CP would have no affect on sperm/egg...CP is a disorder of the muscles, and the two don't have anything to do with each other (unless there's something underlying like Mary's Mom said).
As far as possibilities, well, "where there's a will there's a way." There are books about...technique...one I've heard of is
Enabling Romance, and you or he could do a search for others. Nice of you to look out for your friend

.