I can manually remount /home as the ec2-user by executing these three lines:
$ cd /
$ exec sudo -i
# mount -a
How do I do this in Ansible without rebooting?
Edit:
/home is on a separate volume.
No other users are on the box.
The cd /
removes usage of /home.
The exec sudo -i
kills the ec2-user process, which was using /home, and leaves me logged in as root.
Now I can unmount and mount home without problems.