This is currently done by checking if the location of the user's IP address is the same as the one the user stated in his profile. The location user field for the check will be created during the installation and containts a „Non-EU“ entry and an entry for each EU member state.
The check is performed when the user's clicks on „View and Checkout“. If the check fails, a corresponding error message is shown that explains the problem. Otherwise, the checkout page will be shown and the location is saved in the database.
After the current beta test I'm going to release this as a paid add-on . If you use an 1.2 release of the XPM and want to join the beta test, let me know.