What kind of metamaterial are you looking to create? UWB over what frequency range?
Of course, you should be familiar with the necessarily dispersive behavior of DNG media, as indicated by the Kramers-Kronig relations. Whatever "UWB" is for you, it's likely to be tough.
That's a fairly large bandwidth, but possibly doable. It depends on what kind of technology you are willing to use.
Transmission-line-based metamaterials are probably what you want here, but it depends on whether or not you can interface with the transmission-line modes?