Previously I went through a lot of hoops to figure out how to compile a Teensy version of a burner for my XMEGA. This is a simpler version of those instructions.
And if you just want the hex file for teensy ++ 2, here.
Install CrossPack-AVR to give your Mac avr-gcc. if you are on another OS, install winavr or avr-gcc however you do that.
Close terminal, and open a new one to refresh your environment. Type
avr-gcc --version and you should see something liek this:
avr-gcc (GCC) 4.6.2 Copyright (C) 2011 Free Software Foundation, Inc. This is free software; see the source for copying conditions. There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
Download the LUFA project.
Edit Projects/AVRISP-MKII/makefile. Change MCU like to look like this:
MCU = at90usb1286
CD to Projects/AVRISP-MKII/ and type
drag AVRISP-MKII.hex to your teensy burner window and press reset.
Now, you have a AVRISP-MKII clone!