High-level D&D is traditionally as far-out as Exalted, so to emulate an exalt you could just use the level system (as previously suggested). I also think you could add easier multiclassing, or just free multiclassing in some class.
It's a shame that there are just four roles, otherwise you could use the roles as castes; Dawn = defender, Zenith = leader, Twilight = controller and Night = striker. Maybe Eclipse could be of any role? Another option is to drop the Eclipse caste as a PC-caste. This necessitates that your players aren't in to the Eclipse-caste or doesn't suffer from RPG- related OCD.
The excellency-charms can be dropped. You can assume that they are used or you could say that exalted are just inately superior without having to use excellencies. Anima flares can be based on expenditure of per encounter abilities and daily abilities. When you are out of those, you have the full flare.
Those are the mechanical changes I would make as exaltations are concerned.
Races can switched for different races in Exalted. A PC that is one of those small panda- people can use the mechanical bonuses of halflings, for example. There are many strange peoples in Exalted, pick the one you think will emulate the D&D-race of your choice.
I would put other exalted in NPC-territory, at least for a start.