Comment 12 for bug 1055547

According to

Usage: [xtrabackup_55 [--defaults-file=#] --backup | xtrabackup_55 [--defaults-file=#] --prepare] [OPTIONS]

Default options are read from the following files in the given order:
/etc/my.cnf /etc/mysql/my.cnf /usr/local/mysql/etc/my.cnf ~/.my.cnf
The following groups are read: mysqld xtrabackup
The following options may be given as the first argument:
...
  --innodb-flush-method=name
                      With which method to flush data.
...

it is possible to override innodb_flush_method given to xtrabackup in my.cnf without actually messing with my.cnf perhaps innobackupex should call xtrabackup with a --innodb-flush-method set independently of my.cnf?