Nope, it is not possible thus far.
It mostly boils down to the fact that some properties are not physically plausible in spec gloss workflows and we chose to limit NME due to the already exisiting overall complexity to metal/rough workflows.
That said, you could create roughness from glossiness with (1. - gloss) and you might try to infer the correct metalness value by using some equations @bghgary was using before ???