For having the port 25 restrictions removed, you first of all need to have a valid use case for sending emails to port 25 from EC2. If you have this valid use case, you can submit a “Request to Remove Email Sending Limitations” to the AWS and have the restrictions lifted.
Yes, you can simply use a port other than the port 25. Another alternative could be using an authenticated email relay service. For instance, you may use Amazon Simple Email Services.