Engineering a disulfide bond

[Larry]

My thesis work involves studying the protein-protein interactions
between two enzymes.  One of the interaction domains is a short 69
amino acid coiled-coil motif.  We've cloned and expressed this region
in E. coli but want to engineer a disulfide bond to "close" off the
loop (and make the motif more rigid).  I know that disulfide bond formation
is subject to many variables (correct phi, psi angles, etc.).  Is
there a computer or web-based program that will help me predict where
I can insert two cysteines to create this disulfide bond?  Thanks.