There are a couple of methods to try.
Override stop/start script
In the stop/start script for PostgresSQL I would add the path to this custom version of Python. The start/stop script is here, for example:
/etc/init.d/postgresql. If you add a line towards the top of this script:
You'll override the location that Python is used from.
Add a customization vis sysconfig
Most Red Hat services will look in the directory
/etc/sysconfig for additional customizations. You could try adding the custom
PATH there instead.
Create a file like this:
/etc/sysconfig/pgsql/mycustompath.bash, and add the following line to it (you might need other entries as well):