I've done it...it wasn't too hard to do. Just evade & block all of his moves and only use 4-5 of those stocked reaction commands. Use that set number about 3 or 4 times, and the last time use all 9 with a power at the end. You'll take him down no problem. Oh and to avoid & block, you can either block just before you get hit (gathers way more reaction commands) or aerial dodge, which gets you reaction commands but not as many.
if you wanna take him down quicker trying using knocksmash at the very beginning of the attack, however if you do you really run the risk of him using his "berserk dragon attack", but sometimes you'll get lucky and sometimes you wont...
if he does get the move off, just use reflect
But it's easy...I've done it several times...the time ran about 1-1.5 minutes