Theoretical Mid On-Hit Ezreal Build vs. AP
Early:
Core:
Boots:

Keystone: Stormraider's Surge 9 Flat AD Marks 9 Scaling Armor Seals 6 Scaling CDR Glyphs 3 CDR Glyphs 2 CDR Quints 1 Armor Quint
The build is safe early with Q spam, has both solid and reliable dps and has really strong poke with both Q and E->Q->AA->proc Stormraider's. Solid resistances all around thanks to armor runes, tanky boots and Wit's End. Much less good when kiting's not an option; the best ban is Akali I figure.
I'm not sure what a good alternative for Wit's End would be against an AD lane; maybe to just skip it and get the rest of the build faster instead and maybe get Hexdrinker if you need it.
I'm not that good right now but so far I like this build a lot! I'll post a couple of my other theorycraft builds later too although I'll readily admit I have the most faith in this one.