You can do it with a script, or even from just the /server command, but it's not available in Favorites.
on *:start: {
server irc.network.org -i Nick -j #chan,#chan2,#chan3
server -m irc.network2.org -i Nick2 -j #chan4,#chan5,#chan6
}
It wouldn't hurt for nick to be an option with Favorites, but this can do what you need for the time being.
