The forum software probably uses ftp through php to achieve this
I'm not familiar enough with the ftp functions in php to make this work

If you can figure out how your forum software does this, let me know

I have code ready in UA to look at the addon_zip folder and see if there addon in there that have not yet been scanned to the database

But I'm still working out the interface, it probably will not be in UA 0.7.6