It occurs to me, now that there is an "Insert From URL" script step that appears to work from the web, as I am able to pass it a URL to a document on a web server, and have the file inserted into a container field.
Sooo, if I initiate an upload to a temp folder on the web server via PHP, and then in the same script initiate a filemaker script with the above script step, passing the URL of the temp file as parameter, I should then be able to insert that file into a container of my choosing, without a plugin or a robot machine to grab the temp documents. Then after confirming insertion into the database, the script could delete the temp file from the web server.
Has anyone tried this, or can anyone see holes in the plan. I'll basically have to familiarize myself with PHP to get this working, since I've pretty much only done FM and iwp development to date, but I don't want to go down a dead end if there's some reason this won't work.