Have a look at my answer https://forum.pjrc.com/threads/66913-Can-USB-Mode-be-joystick-only-showing-up-as-multiple-devices?p=279529&viewfull=1#post279529 - that might as well answer your question!
Type: Posts; User: Imagiro
Have a look at my answer https://forum.pjrc.com/threads/66913-Can-USB-Mode-be-joystick-only-showing-up-as-multiple-devices?p=279529&viewfull=1#post279529 - that might as well answer your question!
I think, I can answer that: Look at the file avr/boards.txt. Find your teensy there, and add the entries you need. I think, the file is pretty self-explanatory.
Additionally you might have to...