I also play with ajax. now in the 2012/2013 season. I signed this guy at the start of the game for 875k. he was awful at start but at the 3rd season he's amazing. he scores 11 goals in 12 games with 1 hattrick and 2 MOM. got 4 assist too.
I play 4-3-3 tactic and put him up front together with Necid (Target Man) and swap with Lukaku (adv fwd). I give him adv fwd/att role. If you want him to score more, it is important to set "cut inside" on his wide play instead of normal play. furthermore, with this tactic, he mostly becomes the key man in counter attacking move. he wil become the passer for Necid or Lukaku. at corner, set him for "stand on far post" with your tallest guy "challenge opponent keeper". he often bang a goal from rebound ball.
last but not least, you should be patient with this guy. play him when you meet lower position opponent or in cup macthes. i'm sure at the 3rd season he will become a monster up front.