Ask HN: Need to upload file to many sites. Is it possible to upload only once?

I need to upload a large file to multiple sites, each of which having an upload form that lets me choose a file to upload. In the end, I upload my file to each service separately. The problem is that my connexion is slow and that it takes considerable time to upload everything.

Therefore I would prefer to only have to upload to one service, and from that service be able to upload to any site. Is it possible to do this?