I found a way how to do every trainer achievement in like 30-45 minutes !!!!
First of all you must have unlocked Parallel Quest 43.(i think you unlock this bye completing story missions)
second equip the move(s) you got for your trainer and take him twice with you on PQ 43...
You dont need to hit anything or do any of his tricks.
All you need to do is collect the 3dragon balls and the mission is over (takes like 30-60second)
Keep doing this mission over and over and your progress for your trainer will go up really fast :) !!!
Doing this method i lvl up 3 trainers to MAX in about 2 hours...
Here is a video of someone doing it (exept he is not taking his trainers with him like you schould do )