Get flad AD runes.
Buy a dorans blade or a longsword (for brut). With 1.4 scaling on spear shot, you can start with around 30 extra damage on Q (10 from runes, 3 from masteries, 10 from sword = 23 + 40% = ~33 damage.) A long range, targeted skill that deals 90 damage every 4 seconds...is kinda strong.
Heart seeker strike? WAS useless, complete trash. Now? Same situation as above...13+60% of your AD bonus ( 33 ) and you're talking around 13+16 damage hits...double damage on champs thats not 29, but closer to 60 damage, 3 strikes each, easy 180 damage for a .75 sec channel.
Stack some more AD on him early game, asap. another longsword, brut, last whisper, and max HSS right away, lane with someone who has CC or solo mid. Stun + a HSS is quite deadly in terms of numbers, though I haven't tried it personally - my own successful build on him was a TROLL build the other day, for the lolz. I kept getting focused in lane so I went atmogs with a chalice for MR... finished that game something like 11/3.