How can I pick a savegame location for an HTML build?

I’m trying to make a web customizer that lets the user store their creation on the server for us to be able to open. The problem I’m having is that when I run it in the editor, it saves in the /saved/savegame folder, but when I deploy it on web, it doesn’t save anywhere.

How can I make it so that I can save to a subfolder on the server (through ftp or another way)? I’m using a blueprint-only project, but I’m open to doing some C++ if it’s the ONLY way.