In the dwarven halls, you can use Poison Cloud to kill the 2 guards that take your stuff when visiting the king, thus allowing you free access without that hassle. If you cast Poison Cloud near, but not directly on and NPC, you may be able to kill them (some NPCs are protected from dying) without a drop in reputation.
I have not tried this, but you could kill the guards outside castle Stormfist, to see if that would give you easy access to the castle (save before attempting). Alternately, you can just loot everything (including the throne) while in the castle, and toss it out the front gate before you leave.
