[phenixbb] Constraining carbohydrate conformation

Dear phenixbb users, I wonder how I can constrain the conformation of a NAG-residue during refinement. I have a dataset to 4.2 Angstrom. After refinement some sugars end up in the boat conformation. I would like to run the refinement so that the Asn side chain and the Asn-NAG linkage is refined (using xyz or torsion angle dynamics) but that the NAG-residue itself is considered as a rigid group. Maybe one way of doing this is constraining the bonds and angles of the NAG residue by the defining them as "custom bonds and angles" with sigma=0? Is there a possibility in phenix to generate these constraints from an ideal NAG-residue automatically? Thank you very much for you advice, Kenneth Verstraete