There is API function TogglePetAutocast(index) where index is number of pet ability. So if seduction is pet's 5th ability you can use /script TogglePetAutocast(5);
Another solution is to use addon Zorlen (http://addons.us.to/addon/zorlen-0). It provides various useful function, including function to set pet action autocasts. Example: /script Zorlen_TogglePetSpellAutocast("Seduction", "on");