However for what your asking i donāt think its possible unless its taking vertex data.
Within hlsl you can define a additional struct (besides the input vertex struc) like you have and set it up or even use the values you set within say a vertex or pixel shader function but it has to be called from the function inside hlsl. As far as i know. While its possible to use instancing and bind multiple vertex buffers there are pre-existing calls to use them.
Directly setting into a additional shader struct from the cs side, i donāt think you can do that, maybe but you would probably have to ask one of the main guys if thatās possible.
You can set to shader global variables though directly and just use them that way.