I actually played an epic rogue off and on for 2 years, and he was among the most powerful characters in the party. I never felt outclassed. In part, incredibly high Hide checks and potent magic items helped a lot. This also assumes somewhat reasonable house rules, like we had no epic spellcasting barring what was already statted up in the books (though you could change descriptors to fit) and we also allowed for some homebrew feats to expand various archetypes. That was the last time I was involved in a campaign at 15+, and it was a while ago, though.
One thing my DM did, simply b/c he wanted to, was change a lot of things that had just automatic effects, like Blindsight or Freedom of Movement into a big bonus -- e.g., FoM was a +25 or +30 to resist Grapple. ymmv, but that's what he did.
As noted before, immunities are good. Things w/ flat percentages, like Word Given Form or One With Shadow are also good b/c the epic numbers get ridiculous. Since the character is mobile, avoiding full attacks is good b/c some of the epics can give a ridiculous pounding, so that's another decent tactic. You might also try maximizing Hide and various stealth abilities -- if you're going to move away anyway, you might as well make it work for you.
Finally, as already mentioned, the Epic Deflection feats are actually pretty good, shutting down a Gibbering Orb just by your lonesome is a pretty epic "mundane" feat.