This mod is a simple form list edit that lets you use almost any spell. I'm guessing these spells were blocked from use because of balance, but also because the Xbox 360 couldn't handle magelight on a player while he's riding a dragon.

A few notes:
Conjuration spells wont work or will summon your creature up in the air and it will fall down and die unless you use mods that let you increase the range of conjuration. Whaddya expect when your 500 feet in the air?
Master level spells will not work, I'm guessing because of the casting animations needed.

Installation instructions
Use the Skyrim + Dragonborn ESP if you just have Dragonborn and Skyrim
Use the Skyrim + Dragonborn + Dawnguard ESP if you have Dragonborn, Dawnguard, and Skyrim

You still will not be able to cast certain custom spells, however, BUT if there is a spell that you just have to have while riding a Dragon, load your spell mod, make it require Dragonborn to get access to the following formlists:

DLC2DRRestrictedSpells
DLC2DRAllowedSpells

Delete all the Restricted spells in DLC2DRRestrictedSpells
Add your mod spells and the games normal spells + Shouts in DLC2DRAllowedSpells

Adding spells for MULTIPLE mods will likely require WryeBash, but I have no experience with that.

Enjoy having armies of minions on the ground fighting for you while riding on a dragon!
Or
Using CLEAR SKIES while riding a dragon to clear up bad weather!
Or
Using light magic while riding a dragon at night!