Since you already have an Arduino, - why don't you just learn how to use AVRDude and write the .hex file using ArduinoISP? In the end it will require about the same amount of messing around with the 2 devices, and use slightly less flash(I know, the 1284 has a bunch...) In some ways it might be slightly less convenient, but I have had enough problems with programming breadboarded chips with a serial connection that using the ISP route was just easier.