We use the accounts subsystem to hold /home, then Justin applied the Bind Mount Extensions patch (BME) to remount it read-only in other subsystems, while keeping it read-write accounts/home.

For this, you need to:

 mount --bind -o ro /subsystems/ssname/home

In /etc/fstab:

 /subsystems/accounts/home       /subsystems/arch/home           none    bind,ro

If you use -o remount,(ro|rw) then the change is applied to every mount point (so don't).