Another idea.

The step you can do is:
if specified file doesn't exist you will run your script.
by completion of your script it will create specified file and
it will prevent a new installation by next logging on.

Example code:

code:

---

  $specified_file="c:\install400.ok"
  IF (Exist($specified_file) = 0)
       ; - run installation script or procedure
       ; - possible calls are:
       ; - shell '%comspec% /c x:\software\setup.exe'
       ; - shell '%comspec% /c start /w x:\software\setup.exe'
       ; - shell '%comspec% /c call x:\software\install.bat'
       ;
       ; - script completed. result $specified_file will be created.
       IF (WriteProfileString($specified,"install",@userid,@date+" "+@time) <> 0)
       ENDIF
  ELSE
    $info=ReadProfileString($specified_file,"install",@userid)
    ? "Informative INSTALL: software already installed at "+$info
  ENDIF

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