OK, I just got the trophy. I did it in Exhibition mode P1 vs COM.
To start getting fouls I had to do the following:
1. Set difficulty to Regular or Professional (I was wrong in earlier post, I was playing on Amateur).
2. Edited a team so that all their outfield players had 99 aggression.
3. Got the ball around the penalty area and used Sideways Dribbling (L2 + Right Stick) to tempt the defenders into fouling me.
4. Used Ronaldo for taking free kicks.
It was still a grind to get the trophy because I could only get 4-5 fouls a game and I'm not very good at taking them.
I found this PES 2010 video useful for explaining the basics for taking free kicks, although I didn't use the second player technique.
Hope this helps people get the trophy.