I think it's FAR too early to even consider assist feeding...of course I haven't seen the snake, but 36 days is more of a break than a hunger strike, IMO. My het pied male went off feed last year at 375 grams and didn't eat for 4+ months(not even nearly the longest I've gone through) and he was fine.
What do you suspect is the reason? That he won't eat mice?? Did you ask before you bought?