The only workaround is to export your Inventor assembly to DWF, and then insert the DWF file instead of the IAM. DWF does not have a concept of a "definition", hence does not behave this way (each subassembly is independent, even if identical).
The biggest (only?) downside of this workaround is that you cannot take advantage of Publisher's "update" mechanism.
As a separate point, note that you cannot explode a single part, only an assembly or selection-set containing multiple parts. The parts are exploded away from each other, so "of course" you cannot explode just one.
Autodesk Inventor ETO team
Please apply for Beta testing. Software is available now!
But why can't you even turn off visibility for the separate instances?
It's bad enough that you have to move them together - Or should I say you can't - because you move 1 and they all move, but if you select multiple to move - it fails to move any.