ah you use debug to directly call the alias, that's smart. But it isn't multi server.
since multiple connections may use the same debug target, it could be made to support multiple servers simply by performing /debug on CONNECT (or, more accurately, on ^LOGON) rather than on START. you can also specify an invalid filename such as 'NUL' or 'AUX' to prevent mIRC from writing to disk.
using /debug to spoof a version reply is the smart part, so kudos if you discovered that on your own Dani :P this method is actually close to 15 years old and comes from a time when /debug was undocumented and only took a single argument (on|off to turn on/off debugging to a file named debug.log) but nowadays it has indeed been made much easier with the addition of the -i switch.