You could always search for “Borderlands Drm Free Dlc”. Because the season pass will get you no where.
If you find the drm free edition of the dlcs that comes from the GOTY edition of the game.
You should easily get it installed.
Normally when you got the DLCs just transfer it to an memory stick and then over to your Xbox.
Edit: Here you can find Borderlands 2 DLC DRM Free: Aden34's DRM Free Thread. NEW LINKS! (Bioshock Infinite)