Unfortunately, I do not practice in the D.C. area. I do know that John's Hopkins has one of the best ophthalmology departments in the country and you may want to consider seeing one of their doctors.
The drifting is termed a decompensated phoria. This means that the right eye is turning, usually when the patient is tired, due to a muscle overworking or a muscle that is weakening. There aren't many options aside from weakening the prescription in the other eye, which your ophthalmologist is already doing.
Surgery can straighten out the eye, but this is usually performed in children. In adults, this surgery risks developing double vision permanently.
Because this is typically a condition treated surgically in children, the experts in this area are pediatric ophthalmologists. I know it may seem odd, but you may want to consider being evaluated by a peds ophthalmologist. He or she may be able to provide guidance and give all the options that may be available to you.
I know this is a difficult situation, but if your current ophthalmologist is not sympathetic to your concerns then a second opinion may be very helpful.
I hope this helps...