This is not possible in IWP. The only way you can trip a script trigger is to perform a script that interacts with a layout or layout object set up with a script trigger. To perform that initial script requires clicking a button so there's not much point in getting it to then trip your script trigger.
Just a thought.
I am looking for a way to commit the record after the item is selected from the value list without adding a submit button.
We feel from past performance the users will not hit the submit button on a regular basis. And this could mean 16 or more submit buttons through the process.