Zangetsu focuses on the body he's in, on the spiritual energy around them. It's probably not possible to use Sonído right off the bat, not without possibly injuring Gon's soul. But flash step should be safe enough. He collects the necessary reishi, taking partial control of Gon's legs, and--

FWISH--!

They dash forward, as if teleporting, about 6 feet.

It might be enough to cause Gon to lose his balance, though...