I'm thinking of giving them nets and some NPC party support at this fight, with some time to prepare too.
Whatever you do, do not "give" them an über-powerful DMPC who saves the day. Doing so takes away any sense of accomplishment if they win. They should not feel like spectators in the game of DM's dragon vs. DM's NPC.
"remember: no matter where you go... there you are." - Buckaroo Banzai