Unfortunately, the eBay API for developers does not include the global shipping program. Thus, there's no easy way to get the shipment information without simulating a login to the website.
While this could be implemented just like Amazon is now, I'd need the login information of a working eBay account that has such orders - and to be able to maintain it not just now but forever. Also it's a nightmare to maintain such an implementation (I regret doing the Amazon integration on a daily basis ;-) ) and I'd prefer not to do it as long as it's not part of the eBay API or as long as the tracking information cannot be accessed without being logged in to your eBay account.
Thanks for your understanding!