I don't know, I could see a clever noble supporting Bhelen. He's your dear brother, after all, and you know what his game is now. Keep things in the family, as it is- Harrowmont may be a dear man, but he won't make for a dear king, and your father's will might not mean as much when you learn he sent you away despite believing in your innocence simply to avoid any others looking too deeply at your family (and because the PC needs to become a Gray Warden, but I assume he wasn't made aware of that metagamewise). While helping Bhelen get the throne, you'll see him play even more cards, including some you might have not been aware of, and you'll know even better then it works.
Then you pinch his cheeks, say he's just an adorable little brother-king, take up your title as Lord or Lady Aeducun again, and go save the world (have Ali or Log go die, or take up Morrigan's offer). Come back, and live quietly in your estates for another year or so writing, I don't know, philosophy books about the surface races and how to conquer them all, but make appearances when necessary. Get yourself married so it's obvious that you'll have heir (eventually).
Then, after that year or two, gasp in surprise when Bhelen chokes on a fish-bone that your Master Poisoner self has gotten, make sure Rica and all related to her disappear, and then watch as you get proclaimed King or Queen, oh living Paragon. (If the nobles start dithering about that, I advise my earlier tactic: picking up the Anvil, and hitting it on Assembly's head repeatedly until they name you successor.)
Okay, sure, you can't do it in game and it might not be possible, period... but it would be fun, right?