Shuffle drag objects in custom DnD

Hello,

I'm creating a custom drag and drop question using the free form pick one slide in order to allow more than one target for a drag object. I would also like to be able to shuffle the z-index for the stack drag items. The shuffle option is built into the drag and drop question type, but then I can't allow more than one target.

Does anyone know how I can shuffle the z-order with JavaScript?

Thanks!