Unfortunately, this is not a viable solution, since the Cloudflare Origin CA cert page you link to states
Cloudflare Origin CA certificate to encrypt traffic between Cloudflare and your origin web server
The Origin cert that you can generate on CF and install on your server is issued to CF, not by the origin domain, and will still throw a “This site is insecure” error in browsers that care.
Again, from the linked page:
To ensure greater convenience, security, and performance, Cloudflare recommends an Origin CA certificate over a self-signed certificate or a certificate purchased from a Certificate Authority. With an Origin CA certificate, you can use Full and Full(strict) SSL/TLS encryption mode in the Cloudflare SSL/TLS app without first purchasing a certificate from a Certificate Authority to install at your origin web server.
And a warning note: