Well, if it gets that far, maybe cameos (perhaps defined as any time a character only appears for a single scene or less, in a given a chapter/episode) could be marked with asterisks or italicized text or something, and counted separately from their total appearances number?
So for example, that time when the three Shitennou appear in the episode 44 flashback, it would only count as a cameo for them, but as an appearance for Kunzite since he has a bigger part in the episode. I think most really minor cameos, like when Umino appears in the back of Usagi's class in the first episode of S, can be outright confirmed as a cameo; the back of Naru's head is the only exception I can think of offhand, where I'm not sure if it's a 'real' cameo.
So for example, that time when the three Shitennou appear in the episode 44 flashback, it would only count as a cameo for them, but as an appearance for Kunzite since he has a bigger part in the episode. I think most really minor cameos, like when Umino appears in the back of Usagi's class in the first episode of S, can be outright confirmed as a cameo; the back of Naru's head is the only exception I can think of offhand, where I'm not sure if it's a 'real' cameo.