You could use my avrio package:
http://code.google.com/p/mcu-io/downloads/list
It is licensed GPL v3.
You can then directly access any AVR i/o pin you want by using a PIN_Pb syntax.
i.e.
to set PB6 low you would do:
avrio_digitalWrite(PIN_B6, LOW);
It will do raw port i/o which is around 40x faster than the Arduino routines.
There is lots of information about the i/o primitives in the header file.
There is one catch.
All the arguments must be compile time constants.
i.e.
the pin must be a PIN_Pb define
the value must 0, 1, HIGH or LOW.
There is no modifying of any other files.
Just include the avrio.h header and that it is all.
And as Pito said earlier, the fuses must be set to allow the pins
to be used as i/o pins.
--- bill