You can't, in short no matter what protocol you use, ftp/http/irc/gopher/ssl and so on, your IP is basically connecting you to it, so unless you go via another machine (proxy, bouncer, shell) you can not mask your IP.
Fortunately some IRC servers do over minimal masking, such as quakenet, undernet, dynastynet and probably a whole lot more.
What network is your friend connecting to?