I saw someone suggest the soapy water. That works really well to kill them (wasps and yellow jackets too). As many as you say are in there, the nest has to be really close. Is the stand connected to a tree? A swarm is going to be close to the nest. One maybe two in the stand, I wouldn't say so. Your just not seeing it. Keep looking.

Well according to wikipedia bald-faced hornets will die out during the winter while the queen hibernates. It was 35 this morning and 38 yesterday morning. Im guessing they are done.

I have been told that sevin dust works really well. It is a garden dust that kills insects. Just spray the dust around where you see them going in and they will carry the rest of the dust into the nest and kill the whole nest.