Damage bonuses of this scale can be achieved by a Bard using Inspire Courage with the Dragonfire Inspiration feat (Dragon Magic). This feat provides +1d6 energy damage to allies' attacks for each +1 bonus provided by a Bard's Inspire Courage class feature. By default, the bonus damage is fire damage, but the energy type can be changed via the Draconic Heritage feat, or by being a half-dragon (though that's probably not on the table for an ECL 7 character).
A level 7 Bard only has +1 Inspire Courage, but this can be increased by various things:
- The Inspirational Boost spell (Spell Compendium) provides +1.
- A Badge of Valor (Magic Item Compendium) provides +1.
- The Song of the Heart feat (Eberron Campaign Setting) provides +1.
- The Words of Creation feat (Book of Exalted Deeds) doubles your Inspire Courage bonus.
These are all available by ECL 7; with all of them, you'd end up with +7d6 using a conservative reading of Words of Creation (since Badge of Valor is applied after activating Inspire Courage, it may not be doubled by Words of Creation).