"Ligi has been a great acquisition for us, bringing his experience from Manly and helping to give us depth among our middle forwards," said Warriors recruitment and development manager Tony Iro.
"We've been following Zac for a while and we're excited he has become available in mid-season to give us more options in our outside backs."
Sao and Santo become team-mates at the Warriors almost six years after they were opponents in the NYC grand final in 2011.
Santo scored two tries for the Cowboys in a match which was level 30-30 after 80 minutes before Sao and his Junior Warriors went on to take the title with a golden point extra-time field goal.
Townsville born and raised Santo has featured in the NRL Nines tournament at Eden Park in each of the last four years and played in North Queensland's title-winning side in 2014.
The 24-year-old's only NRL appearance this year was at fullback in the Raiders' season-opening clash against his old North Queensland side in Townsville.
Santo is due to begin training with the Warriors tomorrow.