max > shift registers

hello : ) this is a question regarding max and arduino.

I have just set up a shift register circuit on a breadboard to control a 7 segment display. arduinos pins : 8, 11 and 12 are in use only, and it all works great. in max/msp I send 8 bit (0-255) numbers to the arduino which converts this to serial for the 595 shift registers.

The problem I am having, is that the sketch I obtained from a blog (link below), was only created to demonstrate the shift register concept, therefore all the other ins and outs on the arduino are not available for use.

I am wondering if it is possible to add code to the sketch (in the link), so that all the other pins can be used as well as the 3 pins assigned for the shift registers via serial?

here is a link to the breadboard and arduino sketch
:
http://little-scale.blogspot.co.uk/2008/01/three-595-shift-registers.html

and here is a link to the max msp patch:

http://little-scale.blogspot.co.uk/2008/01/talking-to-3-595s-via-maxmsp.html

thanks for any help on this : )