You can use "Load Plugin From Div" to do an AJAX post and display a result. It is identical to the concept in this tutorial: http://www.webassist.com/tutorials/Dynamic-Dropdowns-with-Data-Bridge-2-0
The only difference is that your plugin shows an error message (or no error) based on the input field on the first page instead of showing a second filtered dropdown list.
This is something I could help with in a premier support ticket.