Arcing really only happens with sharp edges of metal. You can put a spoon in the microwave and it won't arc, microwave ovens have metal screws and metal plates inside and don't arc. If you put a fork in the microwave it'll arc.
If your vial has a cheap flip top then where it attached to the flip top can be sharp. That should be removed anyway since you'll be dragging alcohol wipes across it all the time.
In any case, the coffee cup warmer is the way I'd go. It's cheap and works well.