The TSA says it's okay which means airlines can allow it, not that they *have* to allow it. Jetblue's rules don't allow it, but they probably have more important things to worry about.

Long story short, you'll probably get away with it on Jetblue, but you do run some risk that they will discover it and confiscate it. Since it's an airline rule, not a TSA rule, you
are probably only risking the cost of the cargo.