Multiple deployments, one machine, how to expose them all
Solution 1:
At this time there is no easy way to do this. There is some container support in Juju but network addressability issues still exist. In the near future you'll be able to deploy multiple charms to a single machine using either LXC or KVM containers.
You could fork the WordPress charm and add WordPress Multi User support. It's on the roadmap for that charm but progress is slow.