I built something on similar lines, but settled on a Titan Mauler Barbarian as I wanted to shoehorn in other classes before Dragon Disciple. Specifically, I took Archaeologist Bard (with Fate's Favored) and Lore Warden Fighter for a bonus feat and Combat Expertise without 13 Int. DD progression advances Bard casting.
You could do similar by trading the Titan Mauler levels for Phalanx Soldier levels and keeping two levels in Archaeologist Bard for spells, their luck ability, and skill points. You wouldn't get Rage, but also wouldn't take a -2 to hit when one handing the polearm.
In the long run, I'm questioning whether you'd want more than just 4 levels in Dragon Disciple. Those levels get you +3 to natural armor, +4 to strength, and some nice additional benefits while accepting only one drop to Base Attack and spellcasting. Afterward you could easily go back into either of your base classes or look into a different PrC. Continuing on in DD gets you Con, which is nice, and some ancillary benefits, but aside from the wings at character level 13, PrC level 8... it's pretty meh.