On Simulink, is it possible to add outputs to a vector at the end of each step?

So I've been using MATLAB's RF Mixer: https://imgur.com/1buqXZc

However, I've changed the RF output from Quadrature and In-Phase to Complex Baseband. The overall idea is to generate a signal and then Short Time Fourier Transform it using dsp.STFT. This function requires a time-domain signal specified as a vector so my idea was at each step add the output to a vector and once the steps have finished, input this to a custom built MATLAB Function Block but I'm not entirely sure how to specify 'add value at next simulation step' in a MATLAB function.

I think that would work as long as my step size corresponds to my ideal sample rate.