Can I generate a value based on user input

We have a need for an admin to input an 8-digit code into a virtual attribute named "Challenge" on a user form, run that code through a "generator.exe" on the Active Roles server, then display it in another virtual attribute named "Response".  At this point, when i hit "Save", I can run whatever a user types into the Challenge attribute through the generator.exe and return the "response" code in an error on the red banner or even a policy compliance error near the attribute, but I would love to refresh the form within the Response code in the Response virtual attribute on the form. If there is a way to get the value the user typed into the Challenge attribute and process it without hitting Save and having to re-open the user to see the written response code in the Response virtual attribute, that is what I'm looking for.

I've tried various ways in onGetEffectivePolicy and onCheckPropertyValues and onPreModify, but I can only seem to get the code to display in the WebUI if I write the response code to the Response virtual attribute then re-open the user and see it, or if i throw an error with it.  Anyone have any ideas?