This is quite easily done on while playing the 1st chapter, and even did this solo. I made sure to add player 2 and friendly fire was on before loading the chapter to be safe.
Note: I've completed this game on the XBox 360 where spamming Dragon Swarm has a tendency to freeze the game. I have not encountered this yet on the PS3 version. I don't know if it's fixed, but beware.
I used Magic Gambit + Dragon Swarm (only as much as necessary) and alternated use as I controlled both controllers. Take your time, and between enemy clears, perform a co-op high-five to 'gleam' refill the special gauge faster.
I succeeded with Magic Gambit at about 20 and Dragon Swarm about 15, careful players could probably succeed with those at lower levels.