No, only that it was with Raphael. I doubt it was about selling his soul, considering even back then Raphael said souls with a tadpole were worth very little (likely he knew about the illithid transformation destroying them).
And there is very little narrative value to soul selling. @GrayGhost is probably right, that exploring the Regalia more thoroughly would have tied Gale even deeper to the main plot - the general Act 3 disease might have also contributed to simplifying this portion of the plot. I still would love to see what was originally planned around it because as it is right now, it feels like something is missing.
