You can appened "mysql_read_default_group=$somegroup" to your connect string, and then DBD::mysql should read your my.conf.

my.conf is not being read because the mysql client libraries that DBD::mysql uses don't seem to want to read the my.conf file unless read_default_group is specified. A future version of DBD::mysql will default to "mysql_read_default_group=dbd_mysql" if no other group is specified.