Yeah. Something like
During the rage, your spell list is replaced by: Burning Hands, Fireball, Cone of Cold, <more explodey spells>
Whenever you want to cast a spell, roll a d6. You must cast the spell at that level, but you expend a spell slot 1 level lower. (Ie; roll a 5, cast any spell in a level 5 spell slot, but lose a 4th level slot off your sheet)