I was at KHMT this morning for breakfast and noticed a BD5 jet at a nearby hangar. He had inserted his small Halon extinguisher bottom end forward into an empty instrument hole. Apparently he had fashioned some sort of receptacle for the extinguisher bottom at the sub-panel, then held it in via some sort of friction collar in the panel.
I thought it a novel approach that left the extinguisher at hand height and always near the ready.