This is something I really need to add to my item, as it is a WP Facebook plugin and Fcaebook change things so often, versions are becoming obsolete, so being able to let users know a new version is available is of paramount importance.
Someone asked me about this code, the old link is dead so I’ve put it on github: https://github.com/dtbaker/self-hosted-WP-plugin-updates
No idea if it still works, but someone with more free time is welcome to test it and improve it.
I know this is an old issue, but it’s a big part of why I released my latest plugin. As such, hopefully my reply will be helpful to anyone else researching this issue. I released a plugin called [removed] which is designed to handle auto updates in commercial plugins. Check it out, it might be what you’re looking for!
^ I flagged as your not allowed to link your items in the forums – fyi