Multisite, Cloudflare, Pro Sites, and Subdomains (Oh my!)

This is how I currently have my website.
Someone registers for a free site using the Pro Sites plugin. They get subdomain.domain.com. I force SSL, so they get a Not Secure warning. Cloudflare doesn't allow proper Wildcard SSL unless you pay for the Enterprise platform. I'm having to manually add each subdomain for each user, even though the idea is that as soon as they pay to upgrade ($20/month or so) they will be able to map their own domain name to the website. It's a lot of work for a temporary subdomain.

Isn't there some kind of API or anything I can do to automate this process? Is there another solution I can use to make it work better? I don't HAVE to use Cloudflare, but the protection and speed boost is nice. I just need a true wildcard SSL certificate that works.