Factor analysis with lme?

I'm looking for an example of how (if?) lme can be used with factor
analysis.  By that, I mean modeling the residual variance/covariance
matrix as

Sigma = (Gamma)(Gamma)' + D

where Gamma is a vector (or matrix) corresponding to latent variables
and D is a diagonal matrix.

I have looked around but have not found any examples.  Pointers,
comments, and code are all welcome.

K Wright