I'm really sorry to hear about your condition. Being that your doctor's diagnoses reveals a relation to the sun I wanted to post an article that a member by the name of Longterm found & posted on here long ago. It seems that you are in a very rare cooperative relationship with a dermatologist that is actually willing to try things that you suggest. Please click here for an article related to sun induced exfoliative cheilitis cases documented in El Salvador during the 1950s along with the treatment used to actually cure them.
Some of us have brought this article to the attention of some doctors--myself included--and it was disregarded most of the time. I hope it can help to guide you in the direction towards a cure that will work for you. Exfoliative cheilitis is not only rare, but it's also extremely resilient & variable.