Hey, right up my alley, had one this past fall just that way, they say difficult births do that.
here are two tricks to try, first try to ruff up the nipple, with sand paper or something, it may take after that, cus it is more like mommas teet then.
If that doesn't work, you can't tube forever, the throat will swell and eventually close up. plus there is something about the tube going into the ababmasum or something, anyway.
Try a turkey baster! ALWAYS works for me, just suck the milk from the bottle up into the baster and push it into the back of the throat, he has to swallow.
Try that, it doesnt take too long to feed, and eventually after a few days or weeks, mine always figured it out, when we tried every few days to put the nipple in , one day they just seem to turn that light bulb on and they start sucking. :cboy: