would it be possible to say model your own viewhands and then bind them to the already existing joints from a pair of viewhands?

If they were posed the same way as the CoD ones, yes. The fingers will probably be stuck together after you bind the mesh so you will have to spend some time painting the skin weights on the fingers to keep them independent.

Adding on to what Trem said if the viewhands you get aren't in the same position as the COD rig you can import both models into the scene and match the original rig up to match the new one. Then bind the joints to the new mesh and apply your skin weights. Afterwards you can then reset the joint rotations to make the viewhands move to the correct position.