What do you mean by you only want to set the ban on partyline? Does that make any relevant sense.
Newchanban will match all the ips of the users in the channel and kick all the users on that channel which match that ban. You can use them as 'sticky' or non-sticky see tcl-commands.doc for more information.
You cannot set a ban on partyline. Partyline is a virtual place to interact with linked bots and seperate bots via DCC and it has no relation with channels, so hence you cannot add a channel ban on partyline. I hope I am clear now.
Secondly if you don't want the ban to be always kept on the channel but still in the bots banlist use +dynamicbans on that channel as mentioned and see the 'sticky', or 'stick' command in newchanban for more options.
+Dynamicbans will only ban that user when he joins the channel which he is banned on, if some op removes that ban, then that ban will not be enforced again by the bot (only if +enforcebans is set). It will only reban and place the ban in the channels banlist when that person rejoins the channel the second time and so on....
Hint: If you already have +dynamicbans set and +enforcebans is also there, then -enforcebans to make dynamicbans enabled.