The easiest way to do this is to just lower your difficulty, You don't need to do practice sessions and qualifying only helps make the race even easier. I done this on an AI difficulty of 40 in the karting championship but they can be difficult. So if you have trouble in karts, wait until the end of the season and join a different race team. You do not need to win the sprint races in the karting championships but you do need to win the main races. Also don't be afraid to restart a race, this still lets you get the trophy.