How do I get a 3-phase signal as output, using a single 1D LUT in Simulink, while applying a 3-phase input signal, using the cubic spline interpolation method?

I am using a 1D LUT in Simulink. As input I apply a 3-phase signal, u(3xn) hoping to get an output signal, y(3xn).

Using the linear interpolation method, this is entirely possible. I find it weird how this functionality is not supported with the cubic spline interpolation method, and it seems I need to implement 3 single 1D LUTs, for each phsae. Is there a way around this or am I missing something here?