If it is extended to every Pokemon then there probably will be an option in the Pokemon menu (summary, fly, surf, other hm moves, switch, item, cancel) I'd think it would be called "follow" to send it out and "return" to recall it to its Pokeball. If it is just the starter Pokemon then it would probably be under the options menu or by talking to a person (in-game).
Personally, I doubt it will be limited to starters because the concept IS based around Pikachu, so it would be silly to not at least give you the option to do that with Pikachu as well.