Simscape user here. So first, I would build the thermal network using the thermal domain. It's just a few thermal resistance and thermal masses. With the thermal resistance and masses values (equivalent to R & C) unknown, I would then use the Parameter Estimator App in Simulink Design Optimization to estimate each of the parameters. I think there are 5 unknown parameters to figure out here, instead of 10, since each RC pair represent only one time constant and should scale with each other. As long as the 5 time constants are distinctive enough from each other, you should be able to obtain reasonable estimates this way. More on Parameter Estimation:
You can of course use electrical circuit model in Simscape and use the same parameter estimation method.