What are you trying to do?
I think this might require variables (or .ini if you got alot of servers & channels)
I think that you might want to have mirc log your connections, and then when you type your /server command you mentioned above, it would check and see if you have joined that server recently buy checking either the .ini file or your variables. I am sorry, but I don't have my mIRC on this computer, and I can't access the computer that has it on there at the moment.
If you really need my help, I could do a real quick download, but I hope I don't need to do that *hints to the people online that have their mIRC to post with any help/info for this dude*