All that talk about Fusion with insanely powerful Gated creatures to steal their abilities got me thinking... How about this combo:
1) Gate something preposterously powerful in, that has Epic spellcasting and whatever else you want.
2) Use Fusion to fuse with it. Hell, maybe it is the gated thing that uses the Fusion power, if it has psionics.
3) Use Wish (or Miracle) to emulate the spell Similacrum, making a copy of the fused creature... (to get around the casting time, and you're going to be paying XP through the nose, anyway).
4) Repeat steps 1-3, but have the new creature fuse with the old Similacrum. In this way, you can have a powerful servant with basically every ability in the game.
I'm not sure how you'd determine if it still has enough HD to have the powers you want. I guess if you Gate an advanced version of whatever creature that has double the required hit dice, that would work (Like making a Similacrum of a 28 HD planetar, which would give you a normal planetar).
This is reminding me of the "Breaking the Core" thread.