I dont believe you can modify the LODs of the map object, they are defined by the first cached service loaded.
Therefore, it is my guess you would have to destroy and recreate the map object based on a service that had the correct levels.
I would love to see a solution to this, as my services go from L00 to L20, and i would love to restrict them to L12-L20, but if VE is used, make it L12-L17 as it shuts off here.
Or at least display a "no tile found" png.