Sorry, but that's unlikely. We discourage from relying on GUI configuration in scripting. This would go against that.
And it's not difficult to implement an encrypted password storage yourself in .NET.

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We do not seem to agree on what the library is for :)

RATIONALE:

1. Since the SessionOptions object already has the host name, WinSCP could use the host name/master password pair to look up the session user name & password, as the GUI already does. This avoids the security risk of having the unencrypted password in a script, or storing it on the local machine, where it could be found by a computer repair technician or hacker. A script that wants to use the master password would simply prompt a user to enter it when the script is launched (just like the GUI does).
   
   
2. If the server user name or password ever changes, the user has to tell WinSCP about the change in only one place (the GUI).