How to merge multiple custom regressors into one custom regressor in Matlab?

Question

I want to merge multiple custom regressors as a function in one custom regressor.

Ex:

x1Dot=@(u1,u2,u3,x1)   u2*x1^0.3 + u1 + u3;
x2Dot=@(u2,x1,x2)      u2*x1^0.3 + x1^0.3 + x2;
cr1=customreg(x1Dot,{'u1' 'u2' 'u3' 'y1'},[1 1 1 1]);
cr2=customreg(x2Dot,{'u2' 'y1' 'y2'},[1 1 1]);

After this command:

idnlarxModel=addreg(idnlarxModel,[cr1,cr2]);

I get 2 custom regressors. I need both merged into one custom regressor.