Farm with meteors. If he tries to deny you that, then he will have to be pretty high up in your lane which means an easier jungle gank. Not to mention Veigar has my pick for the best stun in the game making mid ganks all the more effective. You lose out on Q farm, but you can make up for it later in the match. Also, can get it from wraiths occasionally. Every wraith clear is 5 free AP.