I appreciated the sterling work by Gordon (https://projects.drogon.net/raspberry-pi/gertboard/ on the "avrdude" changes to use the "Gertboard ATMega 328P" with a "Raspberry Pi" and all worked well using the MOSI/MISO connections.
However, since fitting a 2.2" LCD screen to the Pi I can no longer use these connections and have therefore been trying to use a Bluefruit EZLink (Overview | Introducing Bluefruit EZ-Link Breakout | Adafruit Learning System) paired with a Pi Bluefruit Dongle (Installing the Raspberry Pi Nano Bluetooth Dongle | The Pi Hut) to upload sketches.
This works perfectly well with the "Arduino IDE" running on a MAC or Windows PC connecting to the "rfcomm" port on an "ATMega ADK" or "Arduino Uno". Using the Pi, however, poses a number of issues where I use the "Gertboard 328p" board setting from your modified "boards.txt" file and upload, again, using the port "rfcomm0" with "AVR ISP" as the programmer (not file upload using the Pi as the Programmer". I get errors "/usr/share/arduino/hardware/tools/avr/bin/avr-ar: Core a: File format not recognised" and "avrdude: AVR device not responding".
Is there an alternative "Arduino IDE programmer" that can be used to achieve this?
Fancy a challenge - many thanks in anticipation.