There isn’t a simple solution.
We had the same problem for the Asterisk/FreePBX module but we didn’t find a very good solution.
We thought about to split the port list into multiple services as you suggested. But with actual implementation the runlevel-adjust will complain about missing services.
At the end we came with a very custom solution: a special property inside the service which control a specific template fragment for opening/closing the ports. Still it doesn’t resolve the problem about listen port.
Maybe switching to systemd in RHEL 7 can help us to simplify a bit the code for service management.