Simulink Parameter Estimation - set linear and nonlinear constraints

Hello Matlab Users. I need to perform an parameter optimization, and I am using the Parameter Estimation in Simulink (Matlab 2016) to do that. I have seen that is possible to set bounds on the value of each single parameter.

Is there a way in the Parameter Estimation, to set linear and nonlinear constraints?For example, if I have two paramters, x and y, whose value changes between 0 and 1, how do I set a constrain, for example, on their sum? (x+y=1)

Many thanks and best regards, Maria Angela