you can add the invite command to your perform
tools --> options --> servers --> connect --> perform
(i.e. /cs invite #channel)
and then use a script to join the channel
on *:INVITE:#channelnamehere: {
/j $chan
}
paste into a new file inside the remotes section of the script editor
(alt + r)
alternatively in tools --> options --> irc you can select auto-join on invite but this will join any channel you get invited too