Ok I figured it out.
First I modified the hosts file and added
This allowed me to configure domain1 and domain2 as virtual hosts in Liferay for my respective instances.
Then I followed the directions to install Liferay in the ROOT directory.
Then I configured my DNS for domain1 and domain2 (using CNAME so no need for a static IP) to point to my bitnami server at xxx.bitnamiapp.com
And voila. Now depending on which domain the request comes from I'm directed to the correct Liferay instance.
NB: the user by default is firstname.lastname@example.org and email@example.com, password is the same one I chose for the default Liferay instance.