Variable Block Size Dilemma

I'm stuck as to how to make this a parameter for the backend.

The postmaster could read a pg_blocksize file and then pass that,
but how could _that_ be set differently when calling the same
copy of initdb?

I'd like to avoid having to set it in the Makefile in the way
that the NAMEDATALEN and OIDNAMELEN variables are set up.

*small lightbulb on*

Would it be acceptable for this to be in a file in the PGLIB
directory?  This could be read in by initdb and then passed along
to the postgres calls.  Does this seem reasonable and/or clean?

Or is there a really obvious way that I'm just not seeing right now?

darrenk