Multiple SMTP servers is a patch I submitted a while ago. I'm 98% sure that it's in the current SVN trunk (not devel-vnext).
Basically, the SMTP servers would be specified the same as the multiple IMAP servers
As for the cookie request, that's fair; except that I think RoundCube is meant to not really store that information in a cookie. Although, it could be a nice little "plugin" that could be developed. As a matter of fact, I'm pretty sure nothing is stored until you log in and even then the session is kept in the database.