Yeah, about your only option would be to always part a channel using a custom alias instead of /part or Shift-click on the channel tab, or right click the channel tab and hitting close, etc.
alias P {
if ($active != $chan) { return }
if ($?!="Do you want to part this channel?" == $true) { part $active }
}
Then, you always use /p to part the channel (or name the alias something better that P). Though it really isn't going to help that much... if you type the alias, you already know you're trying to part the channel.