Port Conflict With Dispatchers

We use shared servers for our application connections... when the database starts and randomly grabs a free port number for the dispatchers, we occasionally run into a port conflict - we also have tuxedo and several other processes that start after the database, that have pre-defined ports assigned. So if the dispatcher grabs port 52452 but say the workstation listener is defined to use that same port - once the WSL starts, we have a conflict.

I know we can pre-assign specific ports to the dispatchers; my concern with doing that is that we currently support roughly 150 customers remotely, all using our standard database configuration; many of these have multiple databases per server - in some cases, up to 10-15 databases. So manually managing specific ports on all of these would be tedious, to say the least... especially if some other third party app comes into play that happens to use one of the ports we selected, and we have to change everyone's ports again.

letting Oracle randomly pick a free port within the defined range.

if we add the known ports that are used in applications that start after the databases (the ones we end up in conflict with) to the /etc/services file - will that prevent the dispatchers from using those ports? Does Oracle search the /etc/services file to find used ports, before it assigns new ones out?

All servers are HP-UX, a mix of PA-RISC based and Integrity. Oracle versions are all 10.2.0.3, with a few at 11.2.0.2. Before anyone suggests it, moving away from shared servers is not an option; our application makes new database connects at every query - so thousands of connects / disconnects every hour; the overhead of spawning a new dedicated connection for every one if these is too great, and significantly slows down the application.