Upload file via URL
Solution 1:
As it is today, there is no way you can do this through the Finder file upload dialog. I also can't find any Chrome Extensions that can do this, but making one shouldn't be too hard. It's times like these you want to be able to do it yourself, right?
The conclusion that made in 2002 here is still relevant:
"Macs cannot do some things using the same techniques as a Windows-based system can."