Sorry for the late reply. I'd wager in the pencil example, "p" is not the feared sound. Generally speaking, if you're able to say a sound it's probably not the one you're afraid of stuttering on. I'd guess it's the "e' that is the feared sound. Vowel sounds are often feared (they're my feared sounds) because vowels are big open sounds and if you really don't hold back and let yourself fully make whatever sound your body wants to make, it can be big and ugly that's what I most want to avoid. If I wasn't afraid of the "e", I would probably say "peeeencil" or "pe-e-e-ncil".