In order for this to work, you'll have to do it with a global script. The script can be called via dialog or using a script attached to the chest (I assume you'll want it to only start running at a certain point in your mod).
If you haven't already done so, I'd suggest getting the guide "Morrowind Scripting for Dummies" (probably available on either TES Nexus or Planet Scrolls, or both). I've got a printed copy of it in a binder that I still refer to occasionally, albeit a rather old version (from back when GhanBuriGhan was still updating it).
Also, as this topic belongs in the TES Construction Set board, I'm moving it there.
