How to set a struct as a Direct3D9 vertex shader constant?

I have a vs_2_0 shader like this:

struct ConstantBuffer
{
    float4 diffuse;
    float4 specular
};

shared uniform ConstantBuffer g_cb : app_constantBuffer;

void PS(out float4 Color: COLOR0)
{
    Color = g_cb.diffuse;
}

The above example is simple, the constant buffer only stores two 4 component colors. I want to set the constant buffer before binding the pixel shader. I do not want to use the ID3DXEffect interface.

The IDirect3D9Device interface only provides methods for setting primitive types...I want to set the entire struct at one time. Is this possible?