Hammer slipping (or "slip hammering") with a regular SA hammer is not too easy. The old timers who used that method had the hammer spur modified to lower and shorten it, then they tied the trigger back and used slip hammering exclusively. In use, the thumb slips off the side of the hammer spur, not off the end.
Both fanning and slip hammering were techniques adopted to make up for technologic deficiency; we now have a better way, called double action.
Jim