I have no experience with OSX, but the principle should be the same.
Try doing an upload using the ArduinoISP to the Attiny2313, for example the blink sketch.
Enable verbose output: File->preference -> check the box: verbose during upload
You can now see how the Arduino IDE handles the upload.
On a Windows machine it looks something like this (stripped fot the path information)
avrdude -p t2313 -c arduino -P COM3 -b115200 -D -Uflash:w:Blink.hex:i
Now you can copy this line to a command line, and substitute the Blink.hex with the hex file you wnat to upload.
A guide to using Avrdude:http://www.ladyada.net/learn/avr/avrdude.html