You can do that with (free) 3rd party software. EventSentry (Light) is one of the products that can do that by monitoring the actual log file and filtering on any text that occurs. There is nothing you have to do on the IIS side - for as long as it logs to the log file.
I actually found a screen cast that walks you through it: https://youtu.be/1Cu_e1PkI2w.
