You can use gravity, at least for most of it.
Make a jumper with 2 liquid fitting. Make one with 2 gas fittings. Have a purged keg, make sure the pressure is released. Have the keg with beer higher than the purged keg. Use the CO2 to start the transfer, then disconnect. Then hook up the gas posts. As the beer drains, the displaced gas goes on top of the beer in the first keg.
Saves CO2, trade off is the longer time it takes. Make sure your jumpers are long enough.