To be honest i wouldnt worry about a very young pup eating its poo because as a puppy they try to eat everything and anything anyway, they are like baby humans learning!!
mine started eating his poo if i wasnt quick enough to pick it up (hes 9 1/2 wks old) but now when hes done a poo he looks at me then i pick it up!
but god, id not let his tounge near me!!! haha!
if it was happening to an older dog id want to stop it asap, i dont think its the hardest bad habit to stop!

:-)