Galvanize light ball Pikachu with fake-out + quick attack.
But Pikachu attracts ground types like a magnet. So I tried Refrigerate, which worked suprisingly well.
I started using FridgeSpeed Pikachu in late ORAS and it's been surprisingly effective (I think the extra power of E-Speed and +2 priority make it better than Fake Out/Quick Attack). The -ate nerf this gen hurt it a bit, but it's also nice to bluff that you're Galvanize - as you say, plenty of players will automatically send out a Ground type when they see Pikachu, especially if you've just KO'd a Flying type with a super-effective E-Speed. It doesn't fare so well in the current incarnation of AAA as Poison Heal: the Metagame as it struggles to take down fat walls and is the glassiest of glass cannons, but it's a fun revenge killer.