Hello Greg,
I've done it sucessfully, that's no problem. I assume that you have also two different elastic IPs pointing to the HANA instances.
Basically there are two ways:
1. Edit your host file, so that the elastic IP of your first instance points to a hostname like imdbhdb1 e.g. and the elastic IP of your second instance poits to another hostname (imdbhdb2 e.g.). When you add these system to the hana studio, you simply use the different hostnames for your AWS instances.
2. Simply add the systems via the different elastic IP. Please keep in mind that you have to do that twice per system - first when specifying the system, second behind the next button after adding the user properties.
I hope that helps!
Best regards,
Karsten