optimize with a membrane protein

[jxs818 AT bham.ac.uk]

Hi All
I am trying to model an membrane protein, and wondered how 
to turn off the optimize routine for selected parts of the 
protein. What I am really after is for Modeller to just do 
the sidechain replacement in the membrane domain and then 
do its normal job (whichs its very good at!) in the more 
variable loop regions.
Cheers all
John