I don't have RSD, but I was an RN and we did put some of these blocks into patients, in the unit where I worked.

People who could not lie on their side in the fetal position were asked to sit on the edge of the bed, bent over towards their knees, to achieve the same bend in their spine.

In fact, most of these procedures were done in this position.

If you think you may be able to hold the position long enough, maybe you could suggest it to your doctor. Just a thought.