File upload from start form

I have a process that will require file(s) to be uploaded in order to start the process. I am creating a custom JavaScript UI and then using the rest API to communicate with Camunda.
I would like to be able to get the form fields from the API and build the form within my application - however, the form fields do not support the type “file”.
I would prefer not to use embedded forms, as I would like to keep all of my UI together in the JS application. Is there another option here for building a form in a custom UI without using embedded forms?