I gave that a shot and it did trigger the update process but much like the install one, it didn't appear to completely work. I don't know if it's significant but when you say ok to the upgrade (on the Notifications page) it goes to the /admin/index.php?confirmplugincheck=1 page. All that it is on it the heading "Upgrading to new version" and the plugin's name. Nothing else and it never redirects away from this page. If I navigate back to the Notifications area it appears that the upgrade has been successful.
I've attached my module.zip file. I'm not a PHP developer by trade, so I expect that there will be some issues in externallib.php (I'm just trying some stuff out) but I figured it would still be able to install as long as that services.php file was correct.
by Duncan Cole.