Yes, it's gross! But I bet he'll remember it for the rest of his life. These are some of the common exceptions to the i before e except after c rule. I picked some words he could spell correctly and tagged them to words he couldn't, which were spelled in the same pattern.
We test, re-test after half an hour, one hour, one day and one week. He writes the word out five or ten times or however many times he needs to. We keep on re-testing.
Please note: spelling is boring, though I've tried to make it exciting, and you shouldn't fixate on your child's poor spelling. Why not try letting them work on the computer with the spellcheck, or voice recognition dictation software. Focus on their creativity.
It must be at least ten times harder for dyslexics to learn spelling, so it's better not to put them through an hour of it in a state of rising hysteria! Ten minutes at a time is enough.