Add them to the Target field in your mIRC shortcut properties.
Example..
BeforeTarget: "C:\Program Files\mIRC\mirc.exe"
AfterTarget: "C:\Program Files\mIRC\mirc.exe" -nouninst -portable
I've done the trial and error thing and every time I put the -nouninst in either the installation shortcut or regular shortcut it still puts the uninstall file in the add/remove programs menu.
Perhaps the uninstall entry already existed from a previous run
while
not using the command line switch? mIRC adds this to
the registry everytime it is run without the -nouninst switch.