I think you can do this very efficiently with AD Model Builder's
random effects module. The software is now freely available at
http://admb-project.org
If you want, you can contact me directly to discuss the model.
Dave
--
David A. Fournier
P.O. Box 2040,
Sidney, B.C. V8l 3S3
Canada
Phone/FAX 250-655-3364
http://otter-rsch.com