a hybrid build could be viable, but I agree with whats been said, full ap would be garbage damage and only for trolling
in addition to LB and perhaps DFG, should get a nashor for the on hit dps buff and for the CDR which you will desperately need. a gunblade would also be key with this build, for the chase and health regen, because you would take considerable harass. guinsoo's rageblade would also work well, you would proc your passive more often from the autos and the stacks would give you some moar ap