Hi Hans
I tried this on Linux, I think that AIX is quite the same:
it is sufficient that you run "setup.sh" from the installation media.
At the prompt, type the directory in which BO4 server is already installed and the installation wizard will detect a previous installation, so it'll propose you to modify/repair/remove the existing installation.
Choose "modify", and, after the language screen you'll have the possibility to select new components to install:
under Instances -> Mobile Services -> Mobile Servers
you'll find what you are searching for !