I don't, other than attempting to use a general minimization package, which I would expect not to work so well without hand tuning of initial guesses. I think

I don't, other than attempting to use a general minimization package, which I would expect not to work so well without hand tuning of initial guesses. I think gsl and chebfun (matlab, unfortunately) can do regression in one dimension but I don't think it can in 2 or 3d (much less general high dimensions).