I have written code with DX9 that uses HLSL pixel shaders and configure their constants with SetPixelShaderConstantF, SetPixelShaderConstantB and SetPixelShaderConstantI.

I've come across this shader, which is PS_3_0, but it is using STRUCT as input instead of float4.

https://github.com/zachsaw/MPDN_Extensions/blob/master/Extensions/RenderScripts/Super-xBR/super-xbr.hlsl

How do I configure that?

Well... after further investigation, it turns out the STRUCT doesn't appear to be used at all; rather, the parameters were defined in the separate included file. Those are standard vectors.