Mirroring the Z axis

I am loading a model with externally supplied matrices, those matrices are produced with a flipped Z-axis.
It's because these models are designed with a Right-Handed coordinate system.

I have been multiplying a "mirror" matrix

Matrix.Scale(new Vector3(1,1,-1))

to all matrices received but this is too slow during load time.

The obvious solution to me seems to be to modify the camera matrix (UNITY_MATRIX_VP in shaders).

Is this possible to do through the standard Unity Camera features or do I have to manually create my VP matrix and supply it in my shaders?

 

I figured it out...
I set the worldToCameraMatrix to a right-handed look-at matrix ported from SharpDX.
A bunch of other, small issues arose as lighting and faces were inverted, simple enough to fix though.