What are you trying to acheive by making the binaries read-only?
All the config files reside in the data directory so there shoudl be a problem making /usr/local/postgres/bin (or whatever you choose to install the binaries) to be a read-only mounted partition. The other option (which is far easier) would be to set the binaries immutable. As root, run this:
chattr +i /use/local/postgres/bin/*
That way only root can remove the immutable flag so they can be changed - if it's a security issue behind your desire to do this then it doesn't matter that root can do that versus your suggestion as root would be able to just remount the partition rw:
mount -o remount,rw /usr/local/postgres
If you can advise why you want them to be read-only then we can make better suggestions.
Cheers,
~p
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