BCLK OC. You can overclock literally any Skylake processor if you have a Z170 motherboard and the proper bios.
It's actually fairly simple and the BIOS is easy to find with a simple Google search.
This site has done most of the work for you.
Actually the G4400 is unlocked and yes it's very simple, even though it's an unusual way to OC for non-k
G4400 has a locked multiplier. You're thinking of the G3258.