Yes it's possible, but you need to configure it manually (just in nginx configs) instead of using the Jelastic dashboard/API SSL feature.
The other point to remember is that because there's 1 IP per container, multiple SSL certificates can only be served via SNI. That may have implications for you depending on what browsers your users use: in most cases it's ok now (old mobile OS and Windows XP are the primary exceptions)
The BindSSL API method allows you to automatically configure one SSL certificate on the externally facing node of your environment (Nginx Load Balancer in your case). If you attempt to BindSSL
multiple times you just replace the existing certificate (not add multiple certificates).
Basically this functionality was built before SNI was widely acceptable, so it was assumed 1 SSL cert. per 1 environment. You can read more about SNI to make an informed decision about whether it will suit your needs here: http://blog.layershift.com/sni-ssl-production-ready/
An alternative for your needs would be to purchase a multi-domain SSL certificate (SAN cert). This lets you contain multiple hostnames within 1 certificate. Since you mentioned that you're our customer, you can contact our SSL team for details/pricing for this option.
If you still want to use multiple SSL certs + serve them via SNI, you will probably need to use the Read and Write API methods to save the SSL certificate parts and config. file(s) on your Nginx node.
Don't forget to restart the nginx service (you can use RestartNodeById for that) after any config. changes.
EDIT: As you mentioned that your end users will have control over this process, you probably prefer to use reload
instead of restart
(see http://nginx.org/en/docs/beginners_guide.html#control).
You can invoke that via Jelastic API using ExecCmdById, with commandList=[{"command": "sudo service nginx reload"}]
But take care if you're allowing end users to upload their own certificates via your application - you need to ensure that what they upload is really a certificate and nothing malicious...