Extreme agoraphobia probably requires more than just simple exposure to improve. I'd recommend working with a therapist. But one thing I am curious about: during exposure, you don't have access to your frontal cortex, that makes sense. But after exposure, do you spend any time reflecting, and reminding yourself that nothing bad actually happened to you? It might be that exercising your frontal cortex afterward could help you learn to cope with the situation in the future. At least, that's what I've done with social anxiety and it seems to help.