For anyone using iOS, I created a workflow for the iOS Workflow app that you can use to add subscriptions. It will retrieve your category list so you can assign the feed to a category.
With iOS’ annoying habit of trying to open RSS links in the News app, I find it best to tap and hold the RSS link. When the menu appears, choose Share and then Run Workflow. Select my workflow and you’re good to go.
Please note that this probably won’t work if you have nested categories. Also, I’ve run into a problem where my workflow won’t show categories that have been created but don’t have any feeds in them yet. I don’t know if this is a Workflow issue or a problem with the API.
Let me know if you have problems, questions, or suggestions.