I'm on a shared hosting without SSH access and I host there 20+ domains. The domains don't have a dedicated public IP address, so I'm using TLS/SNI with a shared SSL certificate for all the domains that I'm able to upload into the hosting administration.
Since I don't have SSH access to the server, I used the Let's Encrypt Manual method (http://letsencrypt.readthedocs.org/en/latest/using.html#manual) on a local computer to issue the certificate.
It took a lot of time to validate all the domains (www + non-www = 20 * 2 challenges) and now the SSL certificate is going to expire (the certificate is only for 90 days).
It is possible to renew the certificate without doing the challenges again? I have the private key for the certificate, so can't they validate the domains based on that?