Such identifiers cannot exist because of the way IRC works. This information isn't supplied by the server without you asking for it (with a /whois). And even if mirc went out of the way /whoising people (and generating a LOT of traffic/lag) the integrity of these internal lists (fullnames, channels) would be compromised (for example, qwerty leaves a channel right after you /whois him; the identifier that returns all channels that qwerty is in would be incorrect, at least till the next /whois on qwerty).
