using LSQLIN, how can i create a cov mtx of the coefficients?

I'm using LSQLIN for a regression and I want to calculate the eigenvalues of the beta coefficients. So i need a cov mtx of the betas. I do not see any output arguments to return the matrix or for the data to build it manually. MVREGRESS has an output argument (VARPARAM) that is the cov mtx of the betas but I can not use MVREGRESS. Looking for similar output from LSQLIN

[Star Strider]

This isn't really an answer, so I'll post it as a comment instead.

Constrained linear regression is a more difficult problem than ordinary least squares regression. (It would be nice if the Optimization Toolbox had some statistical functions, especially since statistics for constrained optimization are different than for the unconstrained optimization used in the Statistics Toolbox.) Constrained estimators and tests in the multiple linear regression model (Part I) discusses the theory and calculations for the constrained linear regression covariance matrix. Note that the X matrix is likely the design matrix (that incliudes a column of ones) although it doesn't specifically mention that in this particular lecture.