Skeetendo

Is it possible to add Pokemon you see in the overworld to your Pokedex? Just Seen, not a full dex entry.
It always bothered me that you could see a Pokemon in the overworld, like Seel in the Pokemon Fan Club or Snorlax outside Vermillion, but it wouldn't register in your Pokedex as seen.

Its a minute detail, but I'd like to implement it into my game if possible.