> any functions in the order by clause must be moved to the select statement (e.g. order by lower(column_name))

What does this refer to? AFAIK, you can invoke functions just about anywhere including in the ORDER BY clause:

    => CREATE FUNCTION some_func (int) RETURNS int AS $$ SELECT $1 + 1; $$ LANGUAGE SQL;
    CREATE FUNCTION

    => SELECT t.* FROM (SELECT 1 AS a) t ORDER BY some_func(t.a);
    a 
    ---
    1
    (1 row)

Are you referring to not being able to reference column aliases in an ORDER BY clause? (work around is to use a subquery)

    => SELECT 1 AS a ORDER BY some_func(a);
    ERROR:  column "a" does not exist
    LINE 1: SELECT 1 AS a ORDER BY some_func(a);