Hmm...going by the interpretation that this works, then the next question would be if effects that say "deal 1d6+1 on your attack" meant 1d6+1 for each bite or only after you made all of your bite attacks and at least one hit. I lean towards only gaining the extra damage once as a more logical interpretation.

L1:
Steel Wind: seems to work well with this interpretation. Do 12d6 to 2 foes.

L2:
Foehammer/Mountain Hammer: From personal experience, DR really sucks for a hydra.
Emerald Razor: Good for this as anything else

L3:
Insightful Strike: If you do Concentration dmg for each bite, it's amazing. If it replaces the whole sequence with 1 check, it's horrible

L4:
Ruby Nightmare Blade: This one seems to work fine. Make the check, deal 24d6.

L5:
Disrupting Blow: 12 chances to prevent a foe to act. Mm.
Dazing Strike: Same as above.
Elder Mountain Hammer: More DR breakage.
Dancing Mongoose: Would 1 more bite per head count? Probably not.
Flanking maneuver: If it's 12 AOO's, awesome. Otherwise eh.

L6:
Desert Tempest: Jackpot!
Irresistible Mountain Strike: 12 chances to prevent a foe to act.

L7:
Avalanche of Blades: This one seems perfect for a hydra.
Hydra Slaying Strike: For when the DM throws your evil doppelganger at you
Ancient Mtn Hammer: DR, yadda yadda, ...
Swarming Strike: Potentially awesome like flanking maneuver.

L8:
Diamond Nightmare Blade: This one should work, and boosts dmg to 48d6
Adamantine Hurricane: Potentially a ton of attacks for 12d6, also should work.
Girallon Windmill: Another one that seems to work pretty clearly

L9:
Strike of Righteous Vitality: This is really too good to pass up

Hmm...looking at it, a warblade/JPM seems best for this situation. Maybe Something like Warblade 1/Wiz 5/Jade Phoenix Mage 10/Abjurant Champion 4 would work well, gets BAB +17 and CL 17.