I'll throw out one more suggestion. tDCS does not penetrate deep in the brain. There is a remarkably simple, non-invasive, cost-free method to stimulate deeper brain structures: it's called (caloric) vestibular stimulation.

You simply lie down in bed with a towell beneath your head, and then put ice cold water (using an eyedropper) into the ear contralateral to (on the opposite side of) your worst pain for 30-60 seconds. The cold stimulation will provoke nystigmus (eyes rapidely darting back and forth) and vertigo; you will probably want to keep your eyes closed, and you definitely do not want to be on your feet during this procedure! Functional imaging shows that the procedure activates a number of deeper brain structures, including the insula which are involved with pain processing.

You can search for the handful of papers exploring this form of stimulation at PubMed. Ramachandran's group claims remarkable and lasting pain relief from a single treatment in several CRPS patients. Most of the papers consist of case reports (an exception being central post-stroke pain). The lack of a definitive study for CRPS invites some doubt, but the procedure is definitely worth a try. Unfortunately, it appears to work much better for upper-body pain, so it hasn't benefitted my wife's condition.

My suggestion is to consider this treatment in combination with tDCS. I see no reason why you can't do the ice-water treatment once a day over an extended period of time.