Server plugin authentication for non-plugin capable client

[Yuriy Vasylchenko]

I needed to modify the MySQL (5.5.28) authentication logic for ODBC client - overriding the native_password_plugin's/old_password_plugin's behavior.
Until lately I was under impression that setting st_mysql_auth::client_auth_plugin=NULL will allow me to use server-side plugin with non-plugin-capable client.
"ERROR 1251 (08004)", http://dev.mysql.com/doc/internals/en/connection-phase.html, and 'sql_acl.cc' told me that I was wrong.

The required change seems to be trivial or about trivial (the only questionable part is the declaration/identification of native_password/old_password capabilities of a plugin, which has the documentation impact). Will it be possible to have that change in 5.5 package?

P.S. Is the inability of a server plugin to read global mysqld variables a deliberate architectural decision, is it a design flaw, or am I completely wrong here and this is possible?