Quoted from the walkthrough on this site:

This way is the longest but you can get almost all of Mog's dances doing it this way. Land your airship at the entrance to the Returner's hideout and jump on the raft on the Lete River. This time the raft will go the way Sabin went the first time and you'll end up near Gau's father's house. From here you have to go thru Sabin's scenerio and hop on the boat To South Figaro in Nikeah. Once in South Figaro it's kinda cool the captain of the ship smuggles you into town in a treasure chest Now you have to go all the way
I'm having a problem getting back into Lete river, though!!! I've tried going through the Returner's Hideout, or enter the Lete River from most anywhere I can get to it!!!

Any ideas? Thanks!