Ah yes, that is one mechanism, vitamin C probably make adrenals work better (which is also why I doubt you have malfunctioning adrenals).
AFAIK, C doesn't influence insulin much, although there are some papers around that show it is necessary for insulin release (at least in scorbutic g. pigs) and some papers that show it blocks insulin release.
Wells, W W, C Z Dou, L N Dybas, C H Jung, H L Kalbach, and D P Xu. “Ascorbic Acid Is Essential for the Release of Insulin from Scorbutic Guinea Pig Pancreatic Islets.” Proceedings of the National Academy of Sciences of the United States of America 92, no. 25 (December 5, 1995): 11869–11873.
http://www.ncbi.nlm.nih.gov/pubmed/8524865.
Bergsten, P, A S Moura, I Atwater, and M Levine. “Ascorbic Acid and Insulin Secretion in Pancreatic Islets.” The Journal of Biological Chemistry 269, no. 2 (January 14, 1994): 1041–1045.
http://www.ncbi.nlm.nih.gov/pubmed/8288558.
Johnston, C S, and M F Yen. “Megadose of Vitamin C Delays Insulin Response to a Glucose Challenge in Normoglycemic Adults.” The American Journal of Clinical Nutrition 60, no. 5 (November 1994): 735–738.
http://www.ncbi.nlm.nih.gov/pubmed/7942581.