Investigating the methods of Wim Hof may yield some useful data points in this search. His book is painfully long winded and self-indulgent, and I'm only half way through without finding any direct methods, but the separate synopsis of the method I've found through google has thus far proven to be both invigorating and grounding when I've tried it.

http://highexistence.com/the-wim-hof-method-revealed-how-to-consciously-control-your-immune-system/