The response you got on the regional forum was pretty accurate. Many LIRR conductors do not know the company's policy toward bicycles, so you MIGHT be able to schmooze a conductor and get some special treatment, or you might not. This works OK if you're just using the train to get to the start of a recreational ride; however, when you need to get to work, you probably want to know before you leave the house.

I think it all depends on how busy the train is. My advice is to dumb down your bike as much as possible so there are no protruding accessories like mirrors, panniers, etc. Conductors will want the aisles and exits to be as clear as possible. Also, I find that showing up with a clean bike helps, as this means the conductor won't be stuck with a muddy train after you get off.

Good luck!