It's not a problem
Looking at "Eating an apple with your nose" as well as a recent Rule-of-Three guest editorial by Chris Perkins, it's not a problem.
Don’t concern yourself with encounter balance. By the time they hit epic tier, the PCs have enough resources to extricate themselves from almost any precarious situation. Throw the kitchen sink at them. If the encounter ends up being too hard, the players will be forced to make some tough tactical decisions, call in some favors, buy time, and put their epic destinies to the test. If the encounter ends up being too easy, the players will feel as invincible as their characters, and that’s equally awesome.
Having just completed a fairly significant campaign changing game at level 25, I can certainly attest to that. While some encounters become narrative speedbumps, our last encounters were: facing high multiple beholder, aboleth, and a kraken. (To start the day out. It kinda hurt. But our fleet survived. Our sea-serpent wasn't quite so lucky.) Then it got worse. The day ended with two PC perma-deaths. The thing is: we were able to emerge victorious through stupidly difficult encounters. The idea of "balance" goes right out the window in high paragon and epic. Instead it's "What monsters feel right for this situation?"
To govern the situation, we turn to Rayla with Gnome stew:
If you’ve ever played or run just about any edition of D&D, but especially 3.x or 4e, imagine this scenario:
Your party of 1st-level PCs all start the game with +5 weapons and 9th-level spells (or for 4e, 20th-level powers).
In the context of the average D&D game, those characters are essentially gods. Sure, they’re fragile, inexperienced gods, but boy are they going to be able to make up for those deficiencies in short order.
Now consider Star Trek, where by default the PCs start out in command of a starship:
Your party of zero-advancement (Decipher Trek’s level equivalent) PCs all start the game with access to a vessel capable of stunning a city block’s worth of enemies from orbit, and they’re armed with weapons that can vaporize any opponent on a successful hit.
In Star Trek, that’s not a problem. Why not? Because the expectations, both mechanically and from a game fiction standpoint, are very different.
Are the PCs going to navigate their starship back to Earth and start stunning cities because it sounds like fun? Almost certainly not, because “that wouldn’t feel like Star Trek.” Similarly, while the PCs may not have amazing ranks in their skills (IE, not be mechanically all that developed as characters), they have godlike powers by way of their technology — and again it’s not a problem, because Star Trek isn’t about those powers, it’s about character development, moral choices, and human drama.
From an older campaign I was in, we were using a depressingly homebrew adaptation of the Marvel universe. In this, our party included someone who could speak the Absolute Truth (me), someone who could stop time, and someone who could invent hyper-tech while stopped in time. As students. We stage-managed a battle between the x-men and one of the major villians because "history was supposed to work out that way." And... it wasn't a problem because our real enemy was: The Dreaded Moral Dilemma. (No, really. moral questions posed the only challenge to our group. They kinda stung.)
An epic level D&D group has transcended the world. Literally. Nations? Cities? Those places that are worth less than a healing potion? If there's a problem that the heroes spot, you bloody post a want-ad in your adventurer's local, and back it with some random spare change you have.
Instead, the fight is about moral choices, decisions that impact the lives of counteless millions living on continents, on other plains, or in the heroes' very own city. Then, choices matter. Because the heroes are beholden to no-one, and because they have the ability to rewrite the world with magic, cash, or swords: their choices matter. Simply figure out the impacts their choices have (besides the big plot BBEGs) and present them back. The fallout from choice will present plenty of drama and conflict. If some battles are too easy? Awesome. they're epic. If some battles are OMGWTF hard? Awesome, they're epic. They have resources. They have hoarded plot coupons from 20 levels in the past. Countless favours that they might be able to draw on.
It's not business as usual. When adventurers can hire adventurers to clear a dungeon... present them with the dreaded Moral Dilemma. A monster they cannot kill with a laser, but one who's cut is all the more keen for that.