how to change progection matrix for some objects

There are a couple of objects for which I want to change the UNITY_MATRIX_MVP(model view projection matrix) or UNITY_MATRIX_MV or UNITY_MATRIX_P.

I can't override vertex program for use custom projection matrix, because i use surface shader and it uses its own vertex program. If i render objects after rendering scene and change camera.projection matrix, it renders out of unity lighting system.

I need set different fov or scale for weapons, but i can't use two cameras