Well, the thing that is shown is that anyone who takes up a coin, with enough will, can contort it into something good. Something that has feeling. Something that would give its "life" for you.
It might depend on which coin was picked up. Remember Lasciel is the called the seducer and web weaver, among other things. Harry speculated she was a "rebel angel among rebel angels." She is being which uses subtlety and manipulation to ensnare her hosts. Her shadow is like the original except she was as mutable as Harry. In other words she could be subtly influenced (manipulated) by her host.
Now take a being like Ursiel. He's all about brute strength and inflicting damage. He's the kind of Denarian who would rather overpower his host than co-opt the poor bastard. So while in theory it might be possible for someone with enough will to control the shadow of Ursiel, that person would not only have to be incredibly strong willed, they would probably have to know in advance of picking up the coin that they would face a devastating psychic attack at the moment they touched the coin.
I think there would be other problems when that individual got into dangerously violent situations. In these types of situations, Lash tried to get Harry to see that calling forth Lasciel was the reasonable thing to do. Ursiel's shadow would use its hosts fear, rage and adrenaline to help it push the host into calling for the true Ursiel.
Lasciel's shadow was the right being to tempt and manipulate Harry, but Harry was the right host to change Lasciel's shadow into Lash, to contemplate her own identity and make her own decisions. It would probably take a whole new bag of tricks to handle a different member of the fallen.