I found this today during my research-
http://www.ncbi.nlm.nih.gov/pubmed/23546884
It showed that LDN has been helpful with CRPS, but unfortunately, the abstract doesn't indicate the dosage used.
I also found this article, indicating memantine, an NMDA antagonist, (name brand Namenda) reduced the pain involved in CRPS:
http://www.ncbi.nlm.nih.gov/pubmed/17314583
Have you tried memantine?