Early clip-ons have a one piece bar-end weight that would have to be removed to insert the typical "expanding dogs" type of mirror anchor. Instead, I had mine machined to fit the CRG clamp ($$).
Later V11 clip-ons (from 2002 LeMans) have a multi-piece weight system that I suspect would have to be removed to use the sliding-dog inserted-anchor common to most bar-end mirror systems.
I wonder what the V11 handlebar bikes use in the ends of their bars (Ballabio, Café Sport, etc)?