Can we get my gestalt E6 character’s dire wolf animal companion/special mount her 21st HD?

In a previous question, I asked about making my strange gestalt E6 character’s mount tougher. I have followed that advice, and as my character is now (among other things) a gestalt of

  • Harmonium peacekeeper 1st/druid 5th
  • beastmaster 1st/ranger-knight of Furyondy 1st

with Devoted Tracker and Holy Mount, so he counts as a 15th-level paladin for the purposes of a special mount, and a 9th-level druid for the purposes of animal companion, which thanks to Devoted Tracker are the same creature: a dire wolf named She-of-Spots.¹ (She-of-Spots also counts as the familiar of a 3rd-level witch thanks to arcane hierophant but that doesn’t affect this question.)

As in the previous question, this is a form of E6 where additional “levels” are gained as gestalt to the previous sets of 6 (which is how I can have Harmonium peacekeeper as my “1st” level, since there is another set² of 6 before it that don’t impact She-of-Spots). Importantly, since this is gestalt, “overlapping” levels that count towards animal companion or special mount status don’t stack, and since it’s E6, those base levels can’t exceed 6th—which I already have for both animal companion and special mount. That also nixes Natural Bond for improving animal companion status. The only reason I am able to achieve effective 9th-level druid and 15th-level paladin status is because of the bonuses provided by beastmaster (+3 levels for animal companion status), Harmonium peacekeeper (+4 levels for special mount status), and ranger-knight of Furyondy (+5 levels for special mount status).

Anyway, all told, my mount has 20 HD—6 HD as a dire wolf, +6 for being the animal companion of a 9th-level druid, +8 for being the special mount of a 15th-level druid.¹ 20 HD is a very interesting number: one more and she’s be an Epic character. As much I despise the Epic rules—and I do—the idea of my pet dog being Epic-leveled in an E6 world is just too amusing not to pursue.

All 3.5e material (including 3.5e-legal 3e material) published by Wizards of the Coast, or from Dragon or Dungeon magazine, is acceptable, as well as all Paizo-published Pathfinder material (Paizo’s 3.5e material. I want some option that simply grants my companion mount (familiar) at least one bonus HD—a real HD, that will allow her to select another (now Epic) feat, not “counting as” or temporary à la inspire heroics. An effect that grants my character a bonus to his effective druid level for the purposes of animal companion would do the trick, for example.

I should level-up a few more times this campaign, so class levels and feats are legitimate, but remember this is E6—prestige classes or feats that require things an E6 character can’t have don’t work. Attempts to “break” the 6th-level limit of E6—say, contracting lycanthropy so that Natural Bond’s +3 druid level bonus applies—are not acceptable.

Suggestions must be something reasonably within player-character control. No outside assistance can be assumed, though, nor stuff like acquired templates that require finding a specific rare monster or whatever. I want stuff I can just pick when I level up or get a feat. Items are acceptable, provided they could be made by an E6 character and provide a continuous bonus.

The mount is a dire wolf—her being canine is pretty important to the story and can’t be changed. Alternative mounts might have more HD, perhaps, and thus reach 21 HD after my existing bonus HD, but unless the alternative is also canine and also has the auto-trip attack that wolves have, it isn’t acceptable. Likewise, polymorph magic, on either of us, isn’t an acceptable answer.

Various forms of extreme cheese—“unleveling,” manipulate form, any kind of infinite/arbitrary loop, perfectly-timed level-ups, are all banned.

  1. The bonus HD from animal companion status and from special mount status have been ruled to stack. This is certainly arguable, RAW, but this is what we’ve gone with—after trying it without and finding the mount a rather anemic contribution to combat.

  2. For the curious, the first set of 6 was commoner, and then another set of 6 devoted to a full-BAB psionic class.