A workaround might be to use this REST endpoint, but would likely require code to execute on the server side somewhere, and therefore likely require you use an externally hosted form that posts to Eloqua. Eloqua does not provide this functionality nor code execution runtime.
You can use import feature or an autosync, in conjunction to the form submission cloud. IM me the specifics.
I work for an Eloqua Partner in Australia. Our tech team has built this function into Eloqua Landing Pages and Eloqua forms for a couple of clients. Once they build one, you can probably use it again and again for different campaigns if you have some HTML skills.
If you'd like an idea on costs involved CLICK HERE to contact us.
Derek BellDirector Customer Success & Marketing
The only solution I see is to have a system in between that will store the file on a server (not in Eloqua), and then submitting all the data+the uploaded file url to Eloqua.