Nope, you cannot trigger the popup (rclick), have the who(is) sent, wait for the servers reply, parse the reply and only then display the matching data in the popup.
You'd need to grab and store the data first
e.g.:
- get data of unknown nicks on me:*:join
- update on nick/join/quit etc
- store this to a hash table or the like
then you could use some
menu nicklist {
$iif(($hget($+(registerednicks,$network),$nick)),drop nick $$1) : -drop command-
}
...which is not reliably anyway, as the user might register/drop the nick in the meanwhile since you grabbed that data