Okay so here is what little I know on the topic.
Yes I have heard a few folks who say they did. Also I know of other folks who were allowed to exceed the 115" limit with other sports equipment that exceeded 115" (one was a pole vaulter who checked a vaulting pole). Certain items are specifically excluded from the 115" limit. I don't read it that bikes are, in fact they specifically are not in at least one airline's policy that I have read in the past. Some are not completely clear in their wording or seem to contradict themselves in different places in their policy.
Gate check agents typically don't whip out a tape measure when you check a bike and a box that is a little over would usually slip right through. An Amtrak box might pass muster as well but would be a little more likely to get denied. Why take the chance? If I had no other choice of boxes I'd cut the box down to the 115" size.