I don't think it will help you much, but the "business" version of WURFL.js includes device physical screen width and height capabilities. It works by comparing the User-Agent from the device web browser against a database of over 45000 devices so is as good as you're going to get in terms of accuracy, but I can't think of an easy way to access that via AppGameKit
You could launch a browser from within your app, and point it to a dedicated page and include a unique reference in the args (deviceid would work). The page needs to be built to capture the WURFL.js results and store them in a database with the deviceID as key. Your app then needs to grab that data via an http request to a custom php script on your server. It may be possible, but it's certainly not going to be very elegant, and will cost you $150 per month for the business WURFL.js, plus running costs of your own server etc.