In the profile settings you can set the channels to join after connecting but to get the app to join a channel with a key and not try to change the channels mode using the key text I do:
JOIN #channame keytext
And this works cos even though it fails to join channel "#:" it does not mess with the channels mode after
So basically the feature request is to update the join code to parse and work with the following instead:
#channame +k keytext, #anotherchanname, #yetanotherchanname
Much simply and no need for strange hacks!