The ones I got could probably clamp around a bar weight if the weight is the right diameter.
The mirrors come clamped to a piece of aluminium with a bolt through it that you screw to the bars anyways. Just unclamp them off that and clamp them onto your weights (if they are the right diameter as mentioned before)
I didn't have bar end weights, just caps so i just took them out and screwed in the ebay bar end mirrors.
I've not noticed any bad vibes etc without weights anyways but i don't spend alot of time at one speed (commuting across city mostly)
EDIT: yeah those cheapos off ebay are the same as what i have.