Are you sure it's fleshy and not a 'sticky bottom' where the yellow poo turns rock hard and is adherent to the wool? This can occlude the anus and prevent anything getting by, but can be gently picked off and the wool trimmed with Swiss Army scissors. When you do this stand well back as if there is a build-up of pressure liquid faeces will come out at speed. If you don't release it the lamb will die.