The ircd I chat on de-ops a regular user on entry to a registered channel when the channel is empty. If it doesn't, most ircd's that I have seen (recent versions) support the command 'SECUREOPS' that is under the help section for the command 'SET', in the ChanServ help directory.
If a user joins who is not on the access list, or otherwise opped, ChanServ will de-op them.
/msg ChanServ SET channel SECUREOPS ON (or OFF)
Try msg ChanServ Help SET for a list of commands to SET, as well as syntax's needed to apply the commands. A msg ChanServ help SET 'command' will show help for a specific command. See what you get. There are other options regarding what you are referring to such as SECURE, and RESTRICTED that fall along those lines too. I think RESTRICTED kicks and bans, or has something to do with identifying with NickServ before entry. The command LEAVEOPS will allow a channel op "take"... leaving op's open for the first join. Sounds like thats what youre trying to avoid though.
Maybe that'll help
Good luck