lme4: constrain sigma to 0

I can write out the specifics without much difficulty.  I want to be 
careful about being absolutely clear in what I say, but, so it will
take 
me a little while.  I will get back to you fairly soon.

Can this be done flexibly so one could set the residual variance to any
value? I would like to fix the residual variance to 1.0 to adjust for
variation in measurement error in the observations as explained in
Raudenbush and Bryk 2002 p.354ff.

Stuart Luppescu <slu at ccsr.uchicago.edu>