I'd like to take the time to point out putting Tristana's Passive on Tristana a second time, making her have 856 AA range 100% of the time at level 18, which outranges Twitch even during his ultimate. She could safely hit towers with no minion support at level 15.
A lot of people have said Kog/Twitch due to having other range buffs, and they would be able to shoot further, but that's on a timer. Double Trist Passive would always be there.
However, this topic is supposed to be about giving a champion a different champion's passive, and for that purpose...
Rengar with Tristana's Passive. Long Range Q-Stabs.